Haselton, M. G. & Buss, D. M. (2001). Emotional reactions following first-time sexual intercourse: The affective shift hypothesis. Personal Relationships, 8, 357-369.
Abstract: This article develops the Affective Shift Hypothesis, which suggests that women experience positive affective shifts following first-time intercourse as a means to facilitate a longer-term, more committed relationship. The hypothesis predicts a negative affective shift in men who pursue a short-term mating strategy; this shift is hypothesized to function to curtail commitment by motivating the man to terminate the relationship.
177 Ss in Study 1 documented sex differences predicted by the affective shift hypothesis. 203 Ss in Study 2, using a somewhat different methodology involving reports of presex and postsex feelings, found that men with high numbers of sex partners, but not men with low numbers of partners, experienced a decrease in their partner's physical and sexual attractiveness following first-time sexual intercourse. In contrast, women, more than men, experienced increases in feelings of love and commitment following first-time sex.