While a significant minority of people practice some form of consensual nonmonogamy (CNM) in their relationships, there is very little published research on how to work competently and effectively with those who identify as polyamorous or who have open relationships. It is easy to let one's cultural assumptions override one's work in practice. However, cultural competence is an ethical cornerstone of psychotherapeutic work, as is using evidence‐based treatment in the services we provide to our clients. This case presents the work of a clinician using both evidence‐based practice and practice‐based evidence in helping a nonmonogamous couple repair a breach in their relationship. We present a composite case representing a common presenting issue in the first author's psychotherapy practice, which is oriented toward those engaging in or identifying with alternative sexual practices. Resources for learning more about working with poly, open, and other consensually nonmonogamous relationship partners are provided.