Psychologically detaching from work in the private setting is crucial to recover from work stress and promotes well-being. Moreover, broad evidence documents negative effects of stress on relationship quality. However, the interpersonal consequences of detachment have barely been studied. We seek to investigate, in daily life, whether and how detachment affects the interaction quality with the romantic partner. We propose that stress impedes detaching from work, and that detachment in turn, promotes individuals’ ability to engage in positive interactions at home, which increases individual and relational well-being. In a first experience sampling study, involving 106 dual-earner couples with young children, detachment mediated the association between work stress and not only the stressed individual’s, but also their partner’s relationship quality. However, positive (affectionate) behaviors did not play a significant role in this process. In a second experience sampling study, involving 53 dual-earner couples with preschool children, detachment was associated with more affectionate interactions, which in turn, predicted lower actor, but not partner evening strain. These results suggest that detachment from work not only affects the working individual’s, but also their close partner’s the perception of their interactions, showing that detachment plays an important mediating role in the stress spillover and crossover process. This emphasizes the relevance of addressing interpersonal processes in the association between detachment and well-being.