In monogamous relationships (i.e., exclusive courtship between two people) individuals agree that certain benefits of the relationship (i.e., sexual contact, material resources, emotional support) may only be shared within the pair-bond. Infidelity thus occurs when one partner defects from this social contract (i.e., forms an extra-pair relationship) while deceiving their partner into believing otherwise. By comparison, consensual non-monogamy (CNM) is a collection of relationship practices and structures whereby partners permit extra-pair sexual contact or intimate attachment. In this theoretical talk, we argue that infidelity and CNM share an evolved motivational framework aimed at satisfying the desire for partner variety, but that each adopts distinct sexual ethics for managing extra-pair romance that produce divergent outcomes in relationship satisfaction, conflict among partners, and personal health. To support our claims, we review empirical work that has examined how people attempt to manage conflict within CNM relationships. We discuss the role of CNM relationship maintenance practices, personality features that predispose people to CNM, and psychological and social barriers (e.g., jealousy, intrasexual competition, sexual health concerns, social condemnation) that hinder people from pursuing or maintaining CNM. Throughout, we consider how CNM, monogamy, and infidelity compare as alternative reproductive strategies, and we propose that CNM and monogamy are more stable strategies for resolving the hardships of sexual conflict compared to infidelity. We conclude by discussing our current, preregistered (osf.io/wex2f) international project studying how individual differences in adherence to multi-partner relationship maintenance practices predict relationship functioning among people with multiple, concurrent romantic and/or sexual partners.

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