Half a century of theoretical accounts, case histories, and evidence implies perfectionism limits the success of psychotherapy and makes it hard for people to participate in and benefit from close relationships. Likewise, intimate relationships are crucial determinants of the success of treatment. However, the extent to which specific types of relationships explain why perfectionism leads to a poorer treatment outcome is unclear. Objective: We addressed this by, first, testing whether the perfectionism traits of self-oriented, other-oriented, and socially prescribed perfectionism hindered symptom reduction in group psychotherapy for depression and, second, assessing the mediating role of romantic love, friendships, and familial love on the effects of perfectionism traits on change in depression. Method: Psychiatric patients (N = 156) enrolled in short-term post-discharge group CBT for residual depression completed measures of perfectionism at pre-treatment, romantic love, friendships, and familial love at post-treatment, and depression at pre-and post-treatment. Results: Multilevel modeling showed that otheroriented and socially prescribed perfectionism were associated with lower post-treatment reductions in depression over treatment and path analysis revealed self-oriented, other-oriented, and socially prescribed perfectionism indirectly predicted lower post-treatment reductions in depression through a perceived lack of quality friendships. Conclusion: Results lend credence and coherence to the Perfectionism Social Disconnection Model in a clinical context and underscore the importance of taking extratherapeutic social disconnection into account when treating perfectionistic patients.