Many individuals suffer negative mental health consequences such as anxiety and depression following separation from a romantic partner and/or co-parenting conflict due to divorce. Consequently, treating the psychological aftermath of divorce and partner separation remains a predominant concern for mental health practitioners. According to family systems theory, high interdependence and low differentiation of self are associated with a lessened capacity for managing anxiety or adapting to stressful events since intense emotions may inhibit the ability to cope. To assess the relationship between differentiation of self and psychological adjustment to separation, 84 divorced adults completed an online survey. Multiple regression analysis demonstrated that a model based on fusion with others, I-position, and emotional cutoff was a statistically significant predictor of lonely/negativity. Bivariate correlation analyses confirmed significant linear relationships between fusion with others, lonely/negativity, and co-parenting conflict. No differences between genders were found. There is a continuing need to develop interventions to address the negative consequences of divorce, help reduce emotional suffering, and encourage healthy co-parenting. Individuals struggling with psychological adjustment post-divorce, or those seeking education for managing the psychological effects of divorce and co-parenting, may benefit from counseling strategies that incorporate an assessment of differentiation of self and psychological adjustment to separation.