From Psychology Today (2013,

College students who recently engaged in casual sex reported lower levels of self-esteem, life satisfaction, and happiness compared to those who had not had casual sex in the past month. And students who recently engaged in hookups had higher distress scores as indicated by levels of depression and anxiety. In contrast to the notion that men are okay with casual sex but women are not, we did not find gender differences in the relationships between casual sex and either distress or well-being. For both men and women, true hookup sex—with a casual stranger rather than a romantic partner or “friend with benefits"—seemed to bode poorly for mental health and self-esteem. Of course, this was a correlational study. We don’t know whether poor mental health caused individuals to be more likely to engage in casual sex or whether, as was shown in studies reviewed by Garcia, poor health resulted from casual sex.

See also: The results do point to a possible “cyclical pattern” in which poor mental health leads to casual sex, which leads to further declines in mental health,

See also: Is relationship satisfaction an important predictor of extradyadic behaviors? Research have showed that levels of general satisfaction with the relationship, sex, and the quality of love and affection are among the best predictors of extradyadic behaviors

And this: even though we propose that past extradyadic behaviors history has an impact on the experience of current romantic relationships, our data were correlational and consequently we cannot make strong inferences. It is possible that someone with an overall high sexual desire and that tends to perceive the quality of intimate relationships to be low, will have a higher tendency to betray their partners during the course of their lives.