Why Men and Women Cheat


By Kenneth Paul Rosenberg, MD

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What the latest science tells us about the brain’s reward systems, love, and sex — and how to prevent an affair from destroying your life

How can I prevent an affair from destroying my life? Whether I am the cheater or the betrayed partner, how can I survive, even thrive, in the wake of an affair? Infidelity provides key insights to find your true sexual and romantic potential and advocates honesty, trust, and integrity–the fundamentals of love.

People often cheat in a haze of delusion, believing that it will bring them real love, help them have better sex, lift their spirits, and boost their sagging self-esteem; however, very often, cheating wrecks relationships and erodes self-esteem. In Infidelity, one of America’s top doctors combines neuroscience, addiction theory, and common sense to explain the three types of cheating: emotional, virtual, and physical; why they’re so prevalent; and how to live in accordance with our values when we are drawn to stray.

Examining what the latest science tells us about the brain’s reward systems, love, and sex, Dr. Kenneth Paul Rosenberg reveals what drives men and women to cheat and what they can do about it. At a time when America’s pornography obsession rises to the level of a competing sexual interest, when is porn a problem, and when does it count as infidelity? And since it is not the act of infidelity alone that destroys a couple, how does any couple prevent growing apart? Through concrete rules addressing these and other vital questions, Dr. Rosenberg guides couples on how to prevent cheating, stop it from progressing, and repair the damage caused by an affair.


author’s note

The patients whose lives I discuss in detail have generously given their permission, and I am completely indebted to each of them. Some of the stories you are about to read also come from people I have known in my personal life. Names and identifying details for all have been changed to protect their privacy. To further disguise the actual patients from my practice, every profile presented in the book is a compilation of at least two, usually three, actual people to ensure that the behaviors of each “book patient” cannot be attributed or linked to any single real, living person. The stories in the book are true and accurate. Nothing in this book should be construed as medical advice, and readers who are wrestling with these issues are urged to seek individualized counseling.


Not everything that is faced can be changed, but nothing can be changed until it is faced.


In American society we tend to draw lines between normal and abnormal, sick and well, “sane” and “insane,” and the addicted versus those with just a few bad habits. In a similar vein we often think there’s a clear division between a “good” spouse and adulterer. I’m here to explain that in reality the differences between these false binaries are not actually so clearly delineated.

Michel Foucault’s The Birth of the Clinic: The Archaeology of Medical Perception documented how the foundations of Western medicine in the nineteenth century were rooted in such distinctions. The new physicians of the 1800s used their medical gaze to create scientific divisions between normal and diseased states that became critical to our understanding of mental and physical illness. But when it comes to matters of the mind, the lines are actually quite blurry. And when it comes to infidelity, most people live in the gray zone.

The great American psychiatrist Harry Stack Sullivan, MD, was fond of saying that even the sickest mentally ill person is much more like us than different. Nowhere is that fragile line between normal and abnormal more evident than with love and sex. With the right drivers, incentives, and opportunities, any of us can become obsessed with another person. After all, isn’t that what falling in love is all about?

Infidelity, defined as a breach in the promise of sexual exclusivity, is the end product of our normal impulses for love and lust gone haywire. Infidelity is a leading cause of divorce in this country. Romantic betrayal can be so devastating that it leads to suicide, homicide, and other crimes of passion. All this, despite the fact that more than 50 percent of “committed” dating people cheat, at least 20 percent of “monogamous” married people cheat, and many of the rest of us supposedly “upstanding citizens” think about it nonstop, although we tend to keep the thoughts to ourselves out of fear of reprisal from our partners and our community. Our adulterous thoughts can sometimes lead us to live in shame, hating ourselves. Although we might tell our partners everything else, our unfaithful thoughts and actions usually remain unspoken. The purpose of this book is to get us thinking about what goes unsaid and to help both adulterers and betrayed spouses alike.

In the pages that follow I quote the scientific literature and explain new discoveries in psychology and neuroscience. I delve into recent findings in genetics that reveal how our genes affect our behavior. I discuss how the new field of epigenetics is demonstrating that not only can our genes affect our behaviors but our behaviors and thoughts can actually change our genes.

My background in treating addiction significantly informs my take on the realities of infidelity. I argue in this book that sex and love are the primordial addictions, meaning our brains evolved to get us addicted to sex and love. These, I argue, are normal addictions. If anything can hook you, it’s lust and romance! After all, the survival of our species depends on it. But in cases of infidelity this irrational exuberance can bring on a truckload of trouble. Understanding our human frailties does not absolve cheaters of responsibility, of course, but it can grant us a new perspective that helps all of us make wiser, more informed choices before we act.

This book is about the role that our brains, our minds (or psychology), and our culture play in infidelity. We’ll learn from biological anthropologists and sociologists who have studied the development of infidelity through the course of human evolution. We’ll hear from psychologists, who explain how modern times are rife with sexual triggers, and from neuroscientists who understand how our brains betray us. All these experts together offer important perspectives to help explain how and why we get in trouble with sex so that we can learn how to better get a handle on desires that lead to destructive behaviors.

In Part I we will explore the science surrounding sex and infidelity with an intimate glimpse into the brain’s reward systems and how they can become hijacked—leading us into destructive behaviors that often include pulling us toward destructive choices, even if we don’t actually enjoy them. In Part II we’ll discuss the different ways people stray, by and large driven by human tendencies toward seeking novelty. In Part III we’ll talk solutions. I’ll offer case studies that provide examples of how couples move past an affair. I’ll discuss guiding principles to help partners discover their true sexual and romantic potential, unhindered by obstacles like ego and insecurity. And I’ll offer practical guidelines to help you avoid—or move out of—the morasses that have ensnared many couples. Although a book about infidelity by nature points out how love and sex can go awry, the take-home message from this book is that passionate love can endure despite our innate tendency to cheat and our built-in drive to destroy the good in our lives.

A Little About Me

As a psychiatrist, I am disinclined to talk about myself. Yet before I discuss my patients, I think it’s only fair to share a little about how I began working with infidelity. As a young doctor I was thrust into treating philanderers because of my dual interests in the scientific study of sex and my specialization in addiction medicine. (Philanderer, by the way, is a term that in common parlance is used to refer to men only. But I’ll use it in this book to refer to women too, particularly as philander in its Latin derivation implies “lover of men.”) Yet long before my professional journey, like many people, my very first experience with infidelity was what I witnessed as a child. This book is not at all about my life, but without a doubt, my own experiences have shaped how I now understand my patients and their families.

My dad co-owned a small meat company in Philadelphia, supplying all the ingredients for Philly’s famous steak sandwiches to local restaurants and the food stands along the Atlantic City Boardwalk. As the company salesman, my dad was rarely home, presumably because he was working so hard. My mother was a devoted wife, kind and joyful, and like many white, Jewish, middle-class mothers in the 1960s, she dedicated her entire being to homemaking and childcare. My mother’s normal maternal worries were made much worse by the deteriorating mental health of my second-oldest sister, Merle, who slowly devolved from a bright, happy child into a hallucinating schizophrenic person.

During the next decade my wonderful sister’s terrible illness plagued her. Merle sought refuge in her room until she could tolerate the hallucinations no longer, and she jumped from her window, three stories above to the concrete pavement. The fall didn’t kill her (although the illness ultimately did), and my beloved sister lived out her life with severe physical and mental limitations. My mother was beside herself with grief and despair. I retreated to my studies and decided to become a psychiatrist to help families like mine. My oldest sister ultimately became a psychologist. Meanwhile my father spent more nights away and, I suspect, sought relief from other women.

I share all this to explain that infidelity exists in a context—in a couple and in a family with its own particular array of hopes and disappointments, triumphs and tragedies. Affairs, new sex, and budding romance can be as much of an escape as drugs and alcohol, and denying affair(s) often reigns supreme. Many families hang onto myths to protect themselves from the truth. In my own family we believed that Dad spent many nights sleeping on the side of the highway. My goal for including this personal information is simply to convey that I both understand how complicated and contextual infidelity is and appreciate how, if my own father could stray, many other decent men and women could easily do the same. As I learned firsthand, infidelity can hit a family like a cluster bomb, perpetually kept a secret and rattling generations to come. On a visceral level many spouses and their children find it impossible to believe, forget, forgive, or reconcile.

Treating philandering spouses became one of my specialties largely by accident. After medical school, medical internship, and a psychiatry residency, during my fellowship at the Cornell Medical Center/New York Presbyterian Hospital, I specialized in sexual disorders and chemical addiction. I studied the early use of Viagra to treat impotence and worked in the field of alcohol, opiate, and cocaine addiction. Early on I was recommended to a public figure who’d had relentless struggles with infidelity. He and his supporters figured that I, an expert in sexual problems (like impotence) and chemical addiction (like alcoholism), could be the one to treat his sex addiction and discreetly and effectively extricate him from his personal and public morass.

In the aftermath of a salacious exposé, he came to my office battered and bruised, mocked and humiliated, and in great pain and anguish. His status and family (whom he loved) might never be the same. I treated him well enough and helped him restore his life. But I knew that if I was going to treat more people with sexual compulsivity, I needed more information and experience. So I went to train with the preeminent sex addiction psychologist, Patrick Carnes, PhD.

Largely derided by academics and my fellow psychiatrists, Dr. Carnes was the first psychologist to popularize the term sex addiction and quickly became one of my closest colleagues. Around the same time the American Psychiatric Association acknowledged that behaviors such as gambling and, possibly, compulsive internet use could be addictive. Although sex addiction is (still) not accepted as a diagnosis, the new terminology of “behavioral addictions” has enabled psychiatrists to think more expansively about the addictive potential of behaviors involving food and sex. The more I studied with Dr. Carnes, the more I realized that he was onto something potentially lifesaving for my patients. Some years later I was pleased to develop and coedit the first academic book about sexual compulsivity and other behavioral addictions.

The book in your hands is, of course, not a textbook, but it does bring the principles I’ve learned in science to the human experiences of sex and love. Today we know so much about compulsivity, infidelity, and the science of the brain. By understanding this science, you can begin to understand yourself, your spouse, and your predicament, granting you important tools for managing desires and behaviors so you are not stuck operating at the whim of your emotions and your impulses.

Caveat Emptor

This book contains no easy path to guaranteed happiness; instead, it offers many reasonable paths away from self-destruction. I’m not about to tell you that you can have your cake and eat it too or convince you that your marriage can benefit from affairs that are based on disrespect, lying, and cheating. That’s hogwash. What you won’t find in the following pages are ten easy steps to marital bliss and sexual nirvana.

What you will find, however, are clear explanations of the science of how your mind works and how and why affairs develop. I will explain how you, your spouse, and even your relationship with one another can survive and even thrive following a secret affair. My patients usually become even stronger as individuals and couples after the discovery of an affair, and I’ll tell you how to make that happen. The father of psychoanalysis, Sigmund Freud, wrote that he could treat neurotic misery, but he couldn’t save people from normal unhappiness. Borrowing from Freud, my job is to rid people not of the normal hiccups and hurdles of relationships but rather of the needless pain and self-torture of cheating.

How do cheaters hurt themselves? The goal of addressing infidelity is not just to promote honesty between spouses but to help us all live lives in accordance with our own ideals. The worst damage that adulterers cause by their infidelity is not only disloyalty to their partner but also betraying themselves through breaking faith with their own hopes and dreams about establishing a trusting, enduring, and loving relationship with someone to whom they’ve pledged their love.

Whether you’ve been unfaithful or have discovered the unfaithfulness of your partner, the goal is to help you avoid impulsively and unknowingly destroying your life, your love, and your family. This book is designed to make you an informed owner of your mind and a conscious participant in your sexuality and your relationship as well as to give you the greatest satisfaction through wonderful sex and genuine, sustainable love.

I will present dozens of real-life cases drawn from the stories revealed in my treatment office by people who, other than being unfaithful, are usually good and decent citizens, as well as stories offered by spouses who were betrayed despite being loving and dedicated partners. The details have been anonymized, and the experiences of two or more actual patients have been merged into each single case study to prevent identification and protect patient privacy. All the stories presented are real and not at all exaggerated, and each of the patients discussed in detail generously gave me their permission to use their stories.

Cheating is an equal-opportunity enterprise, affecting people of all socioeconomic groups, races, religions, sexual orientations, and marital arrangements. In this book I use familiar gender names and pronouns (man and woman, he and she), but this content applies equally to different genders as well as to people of various sexual orientations. Although I often use the terms “spouse” and “marriage,” readers may fill in their own descriptors for themselves, their partners, and their own particular version of a long-term, committed, romantic relationship. This book even applies to relationships without the prerequisite of monogamy because, as I’ll explain in Chapter 1, infidelity has less to do with sex per se and more to do with acts of deception. Therefore, this book is not a diatribe for monogamy. I believe that, with honesty and integrity, people can be happy whether monogamous, nonmonogamous, polyamorous, or even asexual. This book is simply a means to overcome our tendency to deceive and destroy the love in our lives.

Now, let’s get to it.

part one

biology and the basics

Most of us think about love, devotion, and sexual desire as a function of our development, parental teaching, background, and early learning. Or even as a function of something strange and hidden, something we can’t—and maybe don’t even want to—figure out. Scientists, however, have a different view of love, devotion, and sexual desire. They think these emotions largely come from our biology—that evolution created our desires, which are uniquely expressed in different individuals because of other biological and psychological factors. In this section we will explore this argument and try use the science to make some sense of our own bubbling cauldron of feelings around issues of infidelity.

chapter 1

The basics of a cheating heart

We tend to cheat in a haze of delusion, believing that it will bring us real love, help us have better sex, lift our spirits, and boost our sagging self-esteem. Very often, however, cheating ends up wrecking multiple relationships and actually eroding our confidence and sense of self.

We can’t say much about infidelity before defining it. Sexual infidelity is commonly understood to be a breach in the expectation of sexual exclusivity and can be as slight as a kiss or as significant as intercourse. Experts and researchers usually define infidelity as major sexual transgression, requiring a minimum of genital contact. Emotional infidelity, as we’ll discuss in Chapter 5, implies an intense emotional bond with a fair amount of sexual tension and desire. Often the most powerful affairs are those that are both emotional and sexual. Studies have repeatedly shown that heterosexual women perceive emotional infidelity to be nearly as threatening to their relationships as physical affairs. Heterosexual men, meanwhile, tend to worry more about sexual betrayals. Gay men and lesbians tend to find sexual and emotional affairs equally distressing, but studies say they are generally less distressed by infidelity than heterosexuals are overall.

Historically speaking, same-gender couples have shown more tolerance for infidelity and tended to recognize a difference between having a sexual tryst and breaking the trust of a committed relationship. Now that same-sex couples are able to legally marry, however, I have witnessed traditional values supplant the more relaxed attitude that my lesbian and gay patients once had about sex outside their primary relationships. In other words, I’ve noticed in my practice that the gay and lesbian married couples are acting more like straight married couples, with relatively less tolerance of extramarital sex. When surveyed, today’s same-gender couples cite a cheating partner as one of the greatest threats to their union.

My patients struggling with infidelity come from a variety of social circumstances and situations—they have different sexual orientations, are at different ages, and come from many religious, racial, and socioeconomic backgrounds. They are millennials who engage in cybersex and have come of age with internet porn, first-date sex, and friends with benefits. They are women and men in the midst of midlife crises who fear dwindling opportunities in sex as well as in life in general. They also include the elderly, who are living longer and healthier than ever, confronting changes in their bodies and their desires but enjoying the benefits of drugs and treatments that can enhance their sex lives. I have seen religious people who cheat and people who say they cheat despite the fact that they are happy with their spouses. (In surveys over a third of cheating women and over half of cheating men reported that they were perfectly content with their long-term relationships and cheated despite their satisfaction.)

So who can cheat? Anyone! Anytime! Anyplace!

The Three Determinants of Cheating

Over the course of more than two decades in practice I’ve found three main factors that determine adulterous behavior. They are your:

• brain—the neurological structures and chemistry that evolution gave you

• psychology—the mind that you’ve developed through formative experiences that imprint certain ways of thinking about the world, your place in it, and how you think about your sexual/romantic self

• culture—the environment around you, with its varying messages about sex, love, and adultery that inform both your opinions about and opportunities for infidelity

Based on studies that we will discuss in the next two chapters, I estimate that nearly 50 percent of what differentiates cheaters from noncheaters has to do with biological differences in their brain chemicals. This means that more than half of what pushes a man or woman to take the plunge to cheat has to do with both one’s environment and one’s psychology.

The most significant environmental cause is the fact that we can cheat. The easier it is to do, the more likely we will do it. Cheating is not confined to sleazy people. Under the right circumstances it is very easy to turn lustful thoughts into desperate actions.

As we know from studies of chemical addictions, there are several environmental factors that make bad behaviors more doable. Professionals refer to these as the three A’s. If a bad behavior is affordable, accessible, and anonymous, we are more likely to do it. Throughout our discussion here I will repeat and expand on the three A’s and how they shape infidelity.

When it comes to the psychology of cheaters, the biggest factor driving them to stray is the feeling that they’re entitled or deserve to cheat. Research and clinical experience have identified certain personality traits to be associated with this feeling:

1. Narcissism—feeling self-entitled and putting one’s needs first

2. Lacking empathy—not being able to put oneself in another’s shoes

3. Grandiosity—overestimating one’s abilities, especially one’s sexual prowess, and needing validation for one’s abilities as a lover

4. Being impulsive—making important decisions, with major consequences, on the fly

5. Being a novelty or thrill seeker—we will devote two chapters to cheaters seeking novel experiences

6. Having an avoidant attachment style—fearing commitment

7. Being self-destructive or masochistic—a hard-to-grasp psychological concept that I will discuss in detail in the next chapter

What Surveys Tell Us

Infidelity is often cited as the major cause of divorces in the United States, blamed for untold numbers of suicides (particularly among men), and understood to be the root of much unhappiness. But for those who want to stay married after a relationship transgression, it’s helpful to know that there is a silver lining to the statistics. Your relationship does not need to end if you can figure out how to communicate and collaborate after the discovery of infidelity.

Although infidelity may be the event that causes a traumatic rupture to the relationship and can throw an unsuspecting partner into despair, it is not the act of infidelity per se that destroys the couple. Rather, relationships end when couples fail to communicate openly, when they struggle with ambivalence about their relationship and lack the commitment to make their marriage work, and when they are unable to bridge the gap after discovering that they have “grown apart.” These are the issues that prevent repair and reconciliation after the discovery of affairs, and acknowledging these particular issues is the first step toward resolving them.

There are many statistics about cheating. Here are a few highlights. In 2015 the polling site YouGov surveyed about a thousand Americans and reported that 20 percent of men and 19 percent of women admitted to cheating on their partner. YouGov also reported that roughly 25 percent of individuals (22 percent of men and 27 percent of women) said they have taken back a partner after discovering infidelity. According to a survey of sixty-four thousand individuals, heterosexual men are more likely to be upset by sexual infidelity than heterosexual women (54 percent vs. 35 percent), and women are more likely to be upset by emotional infidelity (65 percent vs. 46 percent). However, gay men and lesbian women were equally likely to be upset by infidelity (32 vs. 34 percent). Among heterosexuals, European men and women are more likely to cheat than Americans. And frequent-flyer business travelers are more likely to cheat than those who don’t travel for work. In fact, given that summertime is the peak season for travel, it also becomes a time for new lovers, with the summer months being the peak periods for cheating. Infidelity is not socially sanctioned: 90 percent of adults view sexual infidelity as immoral, and 65 percent view it as unforgivable.

In the past, although male philandering was more acceptable, unfaithful women risked being cruelly ostracized. Economically, psychologically, and socially disadvantaged, women had fewer opportunities to cheat, and even fewer spoke freely about their transgressions. Literature tells stories of women shamed by the scarlet letter (“A” for adulteress), like Hester Prynne, Anna Karenina, and Madame Bovary. But the statistics show that the times are changing.

Since the mid-1970s the General Social Survey of the National Opinion Research Center’s (NORC) Center for the Study of Politics and Society has been monitoring attitudes towards sexual behaviors (including infidelity) among a representative sample of nearly thirty-seven thousand Americans. In the late eighties the survey began tracking adulterous behaviors as well. According to their most recent, as-yet-unpublished findings, which may contain the most scientifically reliable infidelity data in the world, the number of married men who have ever cheated has remained stable at around 20 percent from 1993 through 2016. Among women of all ages, however, there is a definite upward trend, from 10 percent of women cheating in 1993 to 15.4 percent today—a rise of roughly 50 percent over the past twenty-four years.

The economic and social emancipation of women, providing more opportunities to cheat in the workplace along with less stigma, are likely reasons for that percentage spike. In general, women have more than leveled the playing field of breaking marital bonds. Years ago it was most often women who were blindsided when their husbands asked for a divorce. Today women initiate divorce roughly 70 percent of the time, with college-educated women initiating an estimated 90 percent of divorces. Interesting to note is the fact that despite increased rates of adultery, the General Social Survey actually shows higher disapproval of infidelity today than in the 1970s.

Some researchers report observing a rapid escalation of infidelity among twentysomethings in particular. They have predicted that, with the explosion in internet and cell phone use, cheating rates would skyrocket among younger adults, with rates of adultery among young adult women rising to the level of young adult men. In 2015 other researchers (reporting data that conflicted with the General Social Survey findings) found that women cheated nearly as much as men and reported that infidelity is generally on the rise among both men and women as well as among the young, the middle aged, and seniors. For people over sixty cheating has increased since 1991 by at least 10 percent among women and 14 percent among men.


  • "Finally, a brilliant treatise by a leading MD psychiatrist on the Lucifer of relationships: infidelity. Dr. Rosenberg uses the newest data from neuroscience and sex and addiction research to tell us who, why, when and where people cheat, then gives us some clear-headed and sophisticated advice on how to survive, indeed even thrive, after the affair. It's an essential read."—Dr. Helen Fisher, The Kinsey Institute
  • "Straightforward, sex-positive, and comprehensive, Dr. Rosenberg's guide for couples confronting infidelity can help them restore their relationship and sex life."—Dr. Alexandra Katehakis, author of Mirror of Intimacy: Daily Meditations on Emotional and Erotic Intelligence
  • "Filled with common sense tips for those caught in the tangled webs we weave with betrayal. As a working psychiatrist with specialties in addiction and sexuality, Dr. Rosenberg combines the best of current science on the brain, human intimacy, and mental health issues."
    Dr. Patrick Carnes, author of Out of the Shadows
  • "A timely, intimate, authoritative, and always fascinating look at a vexing problem, why people cheat on partners they love."—Peter D. Kramer, author of Ordinarily Well, Should You Leave? and Listening to Prozac
  • "A must-read, insightful, well-written book on a timely and important topic."—Bruce Roseman, MD, Family Doctor, Assistant Professor of Family Medicine and OB-GYN at Mount Sinai Hospital, New York, NY
  • "[An] eye-opening book...Delves deep into the roles that biology, psychology, and cultural norms can all play when it comes to infidelity and its repercussions...A must-read for those who have found themselves dealing with an affair."—Celebrity Parents Magazine
  • "In addition to using data from the therapy sessions with the unfaithful and their wronged spouses Dr. Rosenberg brings to bear a broader perspective from contemporary research in biology, genetics, psychiatry, and so forth to demonstrate 'the science behind sexual betrayal, including the fact that our brains are actually wired to be addicted to sex.'"—New York Journal of Books

On Sale
May 15, 2018
Page Count
288 pages

Kenneth Paul Rosenberg, MD

About the Author

Dr. Kenneth Rosenberg is a board-certified addiction psychiatrist, Distinguished Fellow of the American Psychiatric Association, and a certified sex addiction therapist. He maintains a private practice in Manhattan.

Learn more about this author