With trends in delayed marriage, scholars have begun to explore how a wide range of romantic relationships contribute to health. Although a welcome shift, this largely cross-sectional work ignores potential (in)stability in relationship supports and stressors thought to affect health. Using Family and Community Health Study data on 634 African American young adults, we extend this work by demonstrating the value of a holistic, multidimensional assessment of relationship quality for understanding the link between relationships and health. In addition, however, we also show that there is substantial instability in both the presence and quality of romantic relationships during the transition to adulthood. Importantly, particular patterns of instability are uniquely associated with changes in mental and physical health. Given persistent racial inequalities across both relationships and health, such findings prove theoretically and practically important. In particular, they highlight the need for more contextualized, life course–sensitive approaches in future work.