Although previous studies have reported that the broad autism phenotype is associated with reduced relationship quality within established relationships, understanding how this association emerges requires assessment prior to relationship development. In the present longitudinal study, college roommates with minimal familiarity prior to cohabitation (N = 162) completed the broad autism phenotype questionnaire and intermittently reported on their relationship quality and interpersonal behaviors toward their roommate over their first 10 weeks of living together. Actor-Partner Interdependence Models demonstrated that roommates mismatched on aloofness (one high and one low) had lower relationship satisfaction than those matched on it, with the interpersonal behavior of warmth mediating this association. Because relationship satisfaction remained high when both roommates were aloof, satisfaction does not appear predicated upon the presence of aloofness generally but rather reflects a product of dissimilarity in aloof profiles between roommates. In contrast, although participants reported less relationship satisfaction and commitment with roommates higher on pragmatic language abnormalities, mismatches on this broad autism phenotype trait, and on rigid personality, were less consequential. In sum, these findings suggest that complementary profiles of social motivation may facilitate relationship quality during the early course of relationship development.