Close social partners may contribute to or detract from older adults' health and well-being, in part because daily emotions are closely coupled with the quality of daily social interactions. This study examines variation in this sensitivity to interactions with social partners across the contexts of emotional closeness, interactions with others, and experienced relationship satisfaction across the study period. Using data from the 100-day web-based personal understanding of life and social experiences (PULSE) study, the authors examined the unique contribution of older adults' closest and other social partners to daily experiences of positive and negative affect and considered transitory state-like aspects of sensitivity that vary within individuals across the context of social interactions on that day. Participants in this microlongitudinal study (N = 99, M(age) = 62.3) identified their 5 closest social partners and then reported daily contact satisfaction with those partners as well as positive and negative affect. Multivariate multilevel analysis showed sensitivity of positive and negative affect to the quality of social interactions to vary across participant-defined hierarchies of closeness. Sensitivity to interactions with the closest partner also varied within individuals depending on the quality of interactions with others on that day and also across individual differences in the level of experienced relationship satisfaction during the study period. Together, the findings suggest that emotional responses to social interactions vary according to the context of daily social experiences, as well as accumulated social experiences over time.