Although sexual desire for one’s partner is theorized to serve as a gut-level indicator of partner mate value that motivates investment in valued partners, there is scant empirical evidence to support this hypothesis. Five studies addressed this possibility, examining whether experiencing sexual desire encouraged the enactment of relationship-promoting behaviors and whether perceptions of partner mate value motivated this proposed process. In a pilot study and Study 1, participants relived an activity they experienced with their partner, which was either sexual or non-sexual. Then, participants rated their desire to engage in sex and other non-sexual relationship-promoting activities with their partner (pilot study) and their partner’s responsiveness to personal disclosures. Participants’ enacted responsiveness was also evaluated by judges (Study 1). Results showed that experiences of desire enhanced relationship-promoting tendencies. Using experimental, daily experiences, and longitudinal methods, Studies 2–4 extended these findings, indicating that both manipulated and perceived partner mate value predicted desire, which, in turn, was associated with engagement in relationship-promoting behaviors. These findings demonstrate that sexual desire functions as a mechanism encouraging investment in partners who are perceived to be worth pursuing and retaining.