The onset and escalation of alcohol consumption and romantic relationships are hallmarks of adolescence. Yet only recently have these domains jointly been the focus of sociological inquiry. We extend this literature by connecting alcohol use, dating, and peers to understand the diffusion of drinking behavior in school-based friendship networks. Drawing on Granovette's classic concept of weak ties, we argue that adolescent romantic partners are likely to be network bridges, or liaisons, connecting daters to new peer contexts that, in turn, promote changes in individual drinking behaviors and allow these behaviors to spread across peer networks. Using longitudinal data of 449 couples from the National Longitudinal Study of Adolescent Health, we estimate Actor-Partner Interdependence Models and identify unique contributions of partners' drinking, friends' drinking, and friends-of-partners' drinking to daters' own future binge drinking and drinking frequency. Findings support the liaison hypothesis and suggest that friends-of-partners' drinking have net associations with adolescent drinking patterns. Moreover, the coefficient for friends-of-partners' drinking is larger than the coefficient for one's own peers and generally immune to prior selection. Our findings suggest that romantic relationships are important mechanisms for understanding the diffusion of emergent problem behaviors in adolescent peer networks. (Contains 15 notes, 6 tables, and 2 figures.)