Objective <p>Previous research has shown that prostate cancer (PCa) can affect both patients and their partners. However, research into changes in relational dynamics after PCa remains limited. This qualitative study explored the adaptation process through the lens of psychological flexibility (e.g., relationship values and committed actions) in couples affected by PCa. </p> Methods <p>Participants were recruited through various strategies, including online advertisements and local community posters. Both in-person and remote individual semi-structured interviews were conducted with eighteen couples (36 interviews). The Framework Method was used to analyse the dyadic interview data qualitatively.</p> Results <p>Six main themes and associated sub-themes were generated: (1) psychological responses (initial emotional reactions, recurring thoughts, future perspective, past perspective, present moment awareness), (2) coping styles (responses to thoughts, acceptance, active coping), (3) relationship changes (change in intimacy, relationship re-evaluation, reconnection), (4) relationship barriers (physical challenges, emotional challenges, and social challenges), (5) relationship values (partner identity, partner values, and relationship goals), and (6) relationship commitments (daily activities, planning, partner support).</p> Conclusion <p>After PCa diagnosis, couples’ acceptance appears to influence their adaptation processes in terms of psychological adjustment. </p> Clinical implications <p>By recognising interpersonal and personal experiences, tailored interventions are needed for both patients and their partners. Promoting psychological flexibility may assist couples in maintaining relationship functioning through psychological and behavioural adaptation during the cancer journey.</p>