This study explored 2 key questions at the intersection of care, well-being, and development in romantic relationships. First, what are the links between unmitigated communion (i.e., being overinvolved with meeting a partner's needs to the exclusion of one's own needs) and both partners' relationship satisfaction over time? Second, are there gender differences in the longitudinal links between unmitigated communion and relationship satisfaction? We answered these questions using data from 1,340 couples who participated in the German Family Panel over a 7-year period. Latent change score modeling results revealed that on average, people declined in both unmitigated communion and relationship satisfaction over time, and these declines occurred in concert with each other across each wave: A more rapid decrease in unmitigated communion occurred in tandem with a more rapid decrease in relationship satisfaction. Furthermore, higher initial levels of unmitigated communion predicted a slower rate of decline in relationship satisfaction, and higher initial levels of satisfaction stabilized future declines in unmitigated communion. Lastly, higher initial relationship satisfaction among men predicted a more gradual decline in female partners' unmitigated communion, but women's satisfaction did not predict male partners' unmitigated communion. Overall, this is the first study to demonstrate the codevelopment of and bidirectionality between unmitigated communion and relationship satisfaction in established romantic relationships. Unmitigated communion and relationship satisfaction tend to bolster each other in ways that protect them from steeper declines across time, which may explain why people continue to give in relationships when it is personally costly to themselves. (PsycInfo Database Record (c) 2020 APA, all rights reserved).