IntroductionFailure to provide comfort and care to a romantic partner in a moment of need for support can result in feelings of betrayal and abandonment, and impact trust. This type of relationship trauma is referred to as an attachment injury, which can have negative psychological consequences for the injured partner and for some, it is more difficult to adjust. It appears that forgiveness favors reconciliation in couples who have experienced an attachment injury, whereas unforgiveness can prevent its resolution. But, are the reasons for forgiving or not forgiving a partner associated with adjustment to an attachment injury in injured partners? ObjectivesThis mixed-methods (qualitative and quantitative) study aimed to (1) identify the reasons for forgiving and not forgiving an attachment injury and to organize these reasons into themes, and (2) examine the associations between the forgiveness and unforgiveness themes and the severity of injury-related stress symptoms. MethodA total of 84 participants who forgave and 50 who did not forgive their partner provided reasons for their decision and completed a measure of injury-related stress symptoms. Data were analyzed using thematic content analysis and multiple regressions. ResultsSeven themes of reasons for forgiveness and eleven themes of reasons for unforgiveness were identified. The forgiveness theme Strong partner commitment to repairing the injury on the part of the injuring partner was associated with lower injury-related stress symptoms, whereas the forgiveness theme I understand my partner and/or the context in which the injury occurred was associated with higher injury-related stress symptoms. The themes of reasons for unforgiveness were not significantly associated with injury-related stress symptoms. ConclusionThis study provides a foundation for the development of a psychosocial model of forgiveness and unforgiveness among partners who experienced an attachment injury in their romantic relationship.