Although celebrated for supporting well-being, social relationships can also bring conflict and stress. Despite extensive focus on their bright side—social support—less attention is paid to their dark side—social strain—especially among socioeconomically disadvantaged young adults in high-stress conditions. This study examined how support and strain from parents, friends, and romantic partners contribute to youth well-being, in a Canadian sample of 384 young adults in their early 20s. Participants were on average 20.3 years old (SD = 0.9), evenly split by gender (50% women), 49% without a high school diploma, and 32% with an immigrant parent. Latent class analysis revealed four profiles, splitting the sample roughly in halves. A first half of youth were in two profiles characterized by supportive, strain-free relationships: (1) Wrap-Around Support (high support, low strain from all sources; 16%) and (2) Supported Singles (high support, low strain but not in couple; 30%) profiles. A second half experienced one or more straining relationships and belonged to either (3) Double-Edged (straining parents and partner, but also supportive partner; 24%) or (4) Isolated (straining parents and low support; 30%). Profile comparisons showed that young adults in the Wrap-Around Support profile enjoyed the highest level of well-being, followed by Supported Singles, with the two subgroups in straining relationships showing no differences. A moderation analysis revealed a reverse buffering effect: Stressors weakened the benefits of social support. The results suggest that the “bad” side of relationships can weigh down their “good” side, and that alleviating the burdens of social and other life stressors is as important as strengthening social support for young people to thrive.