I found this blog post fascinating:
It turns out that different people have very different definitions, and they make all kinds of interesting distinctions. For example, some people only think that intercourse “counts” as sex if they have an orgasm. Further complicating matters is the fact that who’s participating in a given behavior influences what counts. Specifically, we seem to hold ourselves to different standards compared to other people.
For example, several studies have shown that people are more likely to label a given behavior as sex to the extent that their significant other did it as opposed to themselves. In a study of 839 college students (96% heterosexual) who were asked whether oral contact with another person’s genitals counted as sex, it turned out that just 36% of women and 39% of men said it did when they imagined themselves doing it . However, when asked to imagine their partner doing the same thing with someone else, 62% of women and 63% of men suddenly viewed it as sex.
From Social Psychological and Personality Science:
Casual sex has become a normative experience among young people, raising concerns regarding its well-being consequences. Prior findings on main effects of casual sex on well-being are mixed, suggesting possible moderating factors. Using longitudinal and weekly diary methodologies, this study examined the moderating influence of sociosexuality, a stable personality orientation toward casual sex, on psychological well-being (self-esteem, life satisfaction, depression, and anxiety) following penetrative (oral, vaginal, or anal) casual sex among single undergraduates. As predicted, sociosexuality moderated the effect of casual sex on well-being on a weekly basis across 12 consecutive weeks, over one semester, and over one academic year. Sociosexually unrestricted students typically reported higher well-being after having casual sex compared to not having casual sex; there were no such differences among restricted individuals. Few gender differences were found. Findings are discussed in terms of authenticity in one’s sexual behaviors.
I suspect that if they did the study for older people they would find similar results. I know I find “casual sex” enhances my psychological well-being.