This four-study investigation examines the role of perceived partner uniqueness (PPU) in determining the immediate communicative and relational consequences of transgressions in romantic relationships. Study 1 reports a psychometrically sound PPU measure distinct from similar constructs. Study 2 reveals that PPU is associated with conflict responses following the discovery of infidelity, which then predict termination intentions. Study 3 involves an experimentally manipulated flirting transgression between one partner and a confederate, witnessed by the other partner, which provides a controlled examination of PPU on partners’ non-verbal immediacy. Study 4 expands and refines PPU measurement, and tests PPU’s ability to predict relational decisions beyond other partner-focused constructs. Results support the utility of PPU as a unique construct with communicative and relational impacts.