Previous research has offered mixed evidence on whether obligation in relationships benefits or harms individuals and their relationships. Given that few studies are prospective and consider multiple close relationships, we used 18-year longitudinal data to model whether obligation is associated with differences in relational and individual well-being over time. Because prior mixed findings may be attributed to differential influences of obligation across development, we also considered age. Light obligation predicted higher levels of relational and individual well-being; substantive obligation sometimes predicted lower levels of well-being. Both types of obligation mostly did not predict "changes" in relationships and well-being over time except substantive obligation predicted slower increases in friend support. The associations between light and substantive obligation were largely uniform across age. The only exception was for substantive obligation and friend support; substantive obligation was associated with a slower increase in friend support only for younger adults (<39 years old). This study extends previous research by examining obligation among middle-aged adults, addressing a critical developmental gap in this literature. Findings suggest that understanding people's obligations toward close others is important not only for their own well-being but also their relationships in adulthood.