We investigate the immediate social context of contraceptive behaviors: specifically, the intimate relationship. We use the Relationship Dynamics and Social Life (RDSL) study (2008–2012), based on a random sample of 1,003 women ages 18–19 residing in a Michigan county. Women were interviewed weekly for 2.5 years, resulting in an age range of 18–22. We test three sets of hypotheses about change over time within a relationship, using relationship-level within-between models, which compare a couple’s contraceptive behaviors across different times in the relationship. First, we find that a couple is less likely to use contraception when the relationship is more intimate and/or committed and that a couple becomes less likely to use contraception over time, regardless of intimacy and commitment. Second, we find that a couple using contraception becomes increasingly likely to choose hormonal over coital methods, but this change occurs as a relationship endures and is unrelated to intimacy and/or commitment. Third, we find that a condom-using couple’s consistency does not decline when there is conflict; rather, consistency of condom use declines over time regardless of the relationship’s characteristics. We also demonstrate that conflict and power imbalance increase reliance on hormonal methods among those using contraception; conflict decreases consistency among withdrawal (but not condom) users; and nonmonogamy increases reliance on condoms and decreases withdrawal consistency. The strong and consistent link between duration and contraceptive behaviors—regardless of intimacy, commitment, conflict, or power imbalance—suggests that the continual vigilance required for long-term contraceptive use is difficult during early emerging adulthood.