The dualistic model of passion (Vallerand (2010) On passion for life activities: The dualistic model of passion. In M. P. Zanna (Ed.), Advances in experimental social psychology (Vol. 42, pp. 97–193). New York, NY: Academic Press) regards passion as a strong inclination toward a self-defining activity that one loves, values, and in which one invests a substantial amount of time and energy. The model proposes two distinct types of passion, harmonious and obsessive, which predict adaptive and less adaptive outcomes, respectively. The present study examined the role of passion for an activity in relationship satisfaction and interpersonal conflict within the purview of the activity using a dyadic approach. We hypothesized that harmonious and obsessive passion would predict adaptive and less adaptive interpersonal outcomes, respectively. Coach–athlete dyads (N = 103) completed a questionnaire assessing harmonious and obsessive passions, relationship satisfaction, and interpersonal conflict. Results revealed both actor and partner effects of harmonious and obsessive passions and generally supported our hypotheses. Future research directions are discussed in light of the dualistic model of passion and interpersonal relationships.