Cheating is not a mental illness. No major diagnostic system, including the DSM-5 or ICD-11, classifies infidelity as a mental health disorder. It is a behavior, not a diagnosis. That said, certain mental health conditions can make infidelity significantly more likely, and understanding the difference between a deliberate choice and a symptom of something deeper matters for anyone trying to make sense of why it happened.
Why Cheating Isn’t a Diagnosis
The American Psychiatric Association’s Diagnostic and Statistical Manual has never included infidelity as a mental disorder. Researchers have specifically investigated whether relationship betrayal produces psychiatric symptoms comparable to recognized conditions, and the consensus is clear: infidelity, by itself, does not reliably produce or stem from a distinct constellation of symptoms that would qualify it as a standalone disorder. It sits in the same category as other painful interpersonal experiences like job loss or marital conflict. These events cause real suffering, but they are life stressors, not illnesses.
This distinction isn’t just academic. Labeling cheating as a mental illness would risk removing personal responsibility from a behavior that, in most cases, involves a series of conscious decisions. Most therapists treat infidelity as a symptom of larger relationship dynamics or individual patterns rather than evidence of psychopathology.
Mental Health Conditions That Increase the Risk
While cheating itself isn’t a disorder, several recognized conditions are strongly linked to infidelity. In these cases, cheating may be less of a calculated betrayal and more of a predictable consequence of the condition’s core symptoms.
Bipolar Disorder
During manic or hypomanic episodes, people with bipolar disorder often experience hypersexuality, which the DSM-5 lists as an example of risky behavior during mania. The drive is not a matter of wanting variety or feeling dissatisfied. It’s a neurological state of elevated energy, reduced inhibition, and distorted judgment that can lead to completely uncharacteristic behavior. People in manic states have described having sex with multiple strangers in a single night, visiting sex workers, or compulsively using dating apps for casual encounters, all while in committed relationships. The guilt and shame typically arrive after the episode passes, sometimes months later, when the person can barely remember what they did.
ADHD
Attention-deficit/hyperactivity disorder affects far more than focus. It fundamentally alters impulse control, reward processing, and sensation-seeking behavior. In a large anonymous survey, people with ADHD who had been unfaithful identified their top motivations as poor impulse control, alcohol-related disinhibition, sensation seeking, and feeling misunderstood by their partner. These aren’t excuses; they’re recognized features of the condition. People with ADHD also report lower sexual and relationship satisfaction overall, possibly because of a general reward deficiency that makes it harder to feel fulfilled. Women with ADHD appear particularly likely to act impulsively on sexual interests, sometimes engaging in behavior they would normally reject.
Narcissistic Personality Traits
People with strong narcissistic traits report more positive attitudes toward infidelity and are more prone to engage in it. The mechanism is straightforward: a sense of entitlement, a constant need for admiration, and a reduced capacity for empathy create a person who feels justified in seeking sexual validation outside their relationship. Their partner’s feelings simply don’t register with the same weight. For someone with grandiose narcissism, affairs may serve a self-regulatory function, propping up their sense of specialness rather than reflecting any dissatisfaction with the relationship itself.
Compulsive Sexual Behavior Disorder
The ICD-11 now recognizes compulsive sexual behavior disorder as an impulse control condition. It’s characterized by a persistent failure to control intense sexual urges over six months or more, leading to repeated behavior that causes significant distress or impairs functioning. Key features include: sexual activity becoming the central focus of someone’s life at the expense of health, work, and responsibilities; repeated unsuccessful attempts to stop; continuing despite clear negative consequences like relationship breakdowns; and persisting even when the behavior no longer brings satisfaction.
Importantly, this diagnosis is not meant to pathologize a high sex drive. Someone who simply has a lot of sex but maintains control and doesn’t experience distress or impairment does not qualify. The diagnosis also explicitly cannot be applied just because someone feels guilt or shame about sexual behavior, or because their actions conflict with moral or religious values. The line is drawn at loss of control paired with real-world harm.
The Biology of Pair-Bonding and Fidelity
Genetics play a surprisingly measurable role in fidelity. A variation in the dopamine D4 receptor gene (sometimes called the “thrill-seeking gene”) is present in about 24% of people. Those who carry at least one copy of the long version of this gene are nearly twice as likely to have had a one-night stand, and when they are unfaithful, they report over 50% more sexual partners outside their relationship compared to those without it. The gene variant is associated with heightened sensation-seeking across many domains, not just sex.
A separate line of research has identified a variation in a gene related to vasopressin, a hormone involved in social bonding. Men who carry two copies of a specific variant (the 334 allele) are twice as likely to report a marital crisis in the past year compared to men who carry none: 34% versus 15%. Their wives independently report lower relationship quality across measures of affection, agreement, and togetherness. These men are also nearly twice as likely to be unmarried. The effect is dose-dependent, meaning one copy of the allele produces moderate effects and two copies produce stronger ones.
None of this means infidelity is genetically determined. These variants shift probabilities, not destinies. But they do suggest that some people are working against a stronger biological pull toward novelty and a weaker neurological foundation for pair-bonding.
Attachment Style and Infidelity Patterns
How you learned to relate to caregivers as a child shapes how you behave in adult romantic relationships, and a large meta-analysis found that insecure attachment is significantly linked to infidelity. People who score high on attachment avoidance (discomfort with closeness, a habit of emotional withdrawal) and attachment anxiety (fear of rejection, hypervigilance about a partner’s availability) both show elevated rates of cheating. The fearful attachment style, which combines high anxiety with high avoidance, had the strongest correlation with infidelity. The dismissive style, marked by emotional independence taken to an extreme, also correlated with unfaithfulness, though more modestly.
Interestingly, the preoccupied attachment style, people who are anxious but not avoidant and tend to cling to their partners, showed no significant link to infidelity at all. This makes intuitive sense: someone terrified of losing their partner is unlikely to risk the relationship through cheating.
How Therapists Actually Approach It
When couples enter therapy after infidelity, most clinicians resist the urge to pin the blame entirely on one person’s psychology. The dominant therapeutic approach treats infidelity as a symptom of something broader in the relationship, not as proof that the cheating partner is mentally ill. Therapists typically work to understand the history of the relationship and the context in which the affair developed, helping both partners reduce blame enough to examine what was happening between them.
This doesn’t mean the person who was cheated on shares responsibility for the affair. Some clinicians argue that systemic approaches can actually cause additional harm to the betrayed partner by implying they played a role. An alternative approach focuses on helping the unfaithful partner examine their own internal conflicts, often rooted in early relationship patterns, without redistributing blame.
When a genuine mental health condition is involved, treatment looks different. If manic episodes are driving hypersexual behavior, mood stabilization becomes the priority. If ADHD-related impulsivity is the core issue, addressing the underlying attention and impulse regulation changes the risk profile. If narcissistic traits are entrenched, longer-term individual therapy aimed at building empathy and examining entitlement patterns is typically part of the picture. In each case, the infidelity is treated as a downstream consequence of the condition, not the condition itself.