This study aimed to integrate elements of Cognitive Processing Therapy (CPT) into the developmental pathway theorized to underlie posttraumatic growth (PTG). PTG theory posits that positive psychological changes can result from the struggle to resolve traumatic experiences. This growth develops through a specific process beginning when a traumatic event violates a person’s core beliefs, or their conceptualization of the world as safe and trustworthy. Violated core beliefs lead to intrusive and then deliberate rumination. Failure to progress from intrusive rumination to deliberate rumination leads to depreciation, or becoming stuck in the traumatic experience. However, empirical investigations of PTG and depreciation have mixed results regarding the extent to which violated core beliefs predict depreciation. This gap suggests an additional route to depreciation exists that is not currently captured by PTG theory. Cognitive Processing Therapy (CPT) offers a possible solution. CPT posits that two cognitive outcomes can occur after traumatic experiences: positive core beliefs can be violated or negative core beliefs can be confirmed. Confirmed core beliefs, called assimilated core beliefs, may offer an additional pathway to depreciation. This dissertation examines a dual-outcome model integrating assimilated beliefs into the PTG pathway using structural equation modeling, a statistical technique that is novel to the PTG line of work. The proposed model was tested among betrayed partners of infidelity. These betrayed partners reported high rates of traumatization and posttraumatic stress symptoms. Prior to model testing, a measure was developed to assess assimilated beliefs after trauma. The Assimilated Beliefs Inventory is presented as a valid and reliable tool. Then, results from model testing indicated that the trauma of infidelity leads to both accommodated and assimilated core beliefs, as expected. Further modeling indicated that accommodated beliefs can lead to both PTG and depreciation while assimilated beliefs only lead to depreciation. These findings indicate that the only route to PTG is through accommodated beliefs. Following this logic, betrayed partners may benefit when clinicians use techniques (e.g., Socratic Questioning) intended to violate core beliefs that were confirmed by their infidelity experience. The remaining model testing indicated that the trajectory toward PTG and depreciation is more complicated than previously considered. Specifically, intrusive and deliberate rumination, which have previously been conceptualized as distinct stages, appear to instead be a reciprocal, bi-directional process. Future research should continue to investigate the PTG pathway, with particular attention on the roles of intrusive and deliberate rumination. Additional implications for research and clinical work are discussed.