Most people enter into intimate relationships with the hope, if not the expectation, that both partners will prove faithful. Yet, we all know the world doesn’t always work that way, and that there are people who just can’t seem to keep from straying. If you’re the one whose partner has strayed, you may blame yourself for somehow failing to hold onto that person. What was it you did, you wonder, that made your partner look elsewhere for relationship—and sexual—satisfaction?

    Susan Krauss    Susan Krauss Whitbourne, Ph.D. is currently a professor of Psychological and Brain Sciences at the University of Massachusetts Amherst. The author of over 160 refereed articles and book chapters and 16 books (many in multiple editions and translations), her most recent popular work is The Search for Fulfillment.

Editor: Talha Khalid

If you’re the one who’s been unfaithful, and you’re willing to confess to your actions, you also know that it wasn’t something you intended to do. You did, at one point, promise to be true to your intimate partner—and you fully meant to maintain that oath. It’s possible that you have a history of this behavior, though, and knowing how hurtful it is to the people you (at least initially) have cared about, you would like to reform your wayward ways.

It may feel like infidelity is an unpredictable outcome in a long-term relationship: Some third party comes along, attracts your partner (or you), and before you know it, things have gone terribly wrong. As the injured party, you sense that your partner has become preoccupied with someone else; as the betrayer, you can’t stop thinking about that other person. If only that person didn’t exist, you believe, all would be well between you and your primary partner.

This irresistible stranger theory, if we were to give it a name, is predicated on the assumption that infidelity arises from outside of the two people in the committed relationship. It is entirely possible that such instances do occur, and that if a particular third person hadn’t emerged onto the scene, the infidelity never would have happened. More difficult to accept is the alternative: That your partner (or you) have the type of personality that is just more easily enticed into a romantic triangle.

As it turns out, getting involved in a triangle may have its roots in the “Dark Triad” traits known to underlie a variety of troublesome behaviors and ways of relating to others. The Dark Triad refers to a threesome of negative personal qualities—narcissismpsychopathy, and “Machiavellianism.” All three involve a tendency to exploit or manipulate others, an inability to experience empathy or regret, and a need to gain power and influence without concern for who gets in your way. Once personality psychologists identified the Dark Triad, a number of previous findings became more understandable; at the same time, it opened new avenues for investigation.

The study of infidelity is one area explored in terms of its relationship to Dark Triad traits. People high on these traits are, as University of Central Lancastershire (UK) psychologist Gayle Brewer and colleagues (2015) describe, less able to form strong relationship commitments, more likely to deceive others, and more likely to betray their trust. They also tend to have more of a wandering eye for alternative partners. The Brewer et al. study focused, in addition to the Dark Triad’s relationship to infidelity, on the desire for revenge by people who’ve been the victims of a cheating partner. We’ll get to those findings shortly, but as you might imagine, those high in Dark Triad traits don’t respond well to an unfaithful partner.

The British team conducted an online study of women ranging from 18 to 42 years (but primarily toward the younger end of that spectrum), almost all of whom were involved in a long-term romantic relationship. Infidelity was measured by a kind of 360-degree approach in which participants reported on:

  • the extent to which they had engaged in their own acts of infidelity such as going out on a date or having a one-night stand with someone outside of their primary relationship;
  • whether they would consider doing so in the future; and
  • the likelihood of whether their partners would do so.

As expected, the Dark Triad qualities predicted each of the three aspects of infidelity, but the findings were particularly strong for narcissism and psychopathy. In terms of high levels of narcissism, the authors concluded:

“These women may believe that they can engage in infidelity but avoid detection by their partner, and thus avoid the consequences (e.g., conflict, retaliation, relationship dissolution or reputational damage) associated with infidelity” (p. 124).

High scores on the antisocial aspects of psychopathy were related to higher scores on intentions to be unfaithful, along with feeling susceptible to their partner’s infidelity. Thus, women who tend to act out against others are less trusting of others, and themselves. The authors take care to note that this form of psychopathy ("psychopathy 2") is not what we normally associated with personality psychopathy (a lack of remorse and the tendency to exploit others) but the tendency to commit risky or even criminal acts.

The second part of the study investigated the relationship between Dark Triad traits and revenge. As expected, the two were positively related. However, of all the individual traits to emerge as related to the desire to punish an unfaithful partner, it was again that risky and perhaps criminal form of psychopathy that played the largest role. The avenger, as it turns out, is someone who acts impulsively, doesn’t care about the consequences, and will do almost anything to drive out angry feelings. This is “hot” revenge, as compared to revenge “best served cold"—and it can have more dangerous results.

Returning to the question of how you can predict infidelity, we can now see that not all the Dark Triad traits would be able to predict who will and who will not cheat. Instead, one's focus should be on these three:

  1. Narcissism. No surprise here. People who believe that they are entitled to whatever they want will behave accordingly. If that whatever isn’t you, you may suffer the fate of the cheated-upon partner. If this characterizes you (and you’re willing to admit that it does), then even if you value your relationship, it will be an uphill battle to convince yourself that you can’t have whatever you want because you want it.
  2. Acting out. Being high on the antisocial or secondary form psychopathy is not ordinary psychopathy involving a lack of moral compass, but instead is the tendency to show anger in a destructive manner.
  3. Low intimacy. The unfaithful partner in a romantic relationship may not be romantic at all. They may become infatuated, but they are unable to get truly close to a relationship partner. As the Brewer et al. team states, “Increased susceptibility to infidelity may reflect…negative affect, anxiety and low self-esteem” (p. 124). This is similar to people with an insecure attachment style, who avoid getting close because they do not feel safe in an intimate and committed relationship.

Infidelity is a complex feature of close relationships, reflecting a combination of the personalities of the partners and the qualities of the others who may provide temptation. This study, while involving only female participants, and most of them young, is the first to show that above and beyond simple narcissism, another form of psychopathy exists, involving riskiness and acting out rather than simple cold-blooded remorselessness—and it can add an important predictor to the equation.

Finding fulfillment in long-term relationships may involve, from time to time, handling the uncomfortable feelings that come with the desire to cheat, the feeling that your partner is cheating, or some combination of both. This three-part checklist can provide you and your partner with some useful guideposts.