Social interactions shape relationships between individuals in group-living animals, and may occur more frequently with specific group members. Affiliative interactions such as allogrooming are expected to be associated with benefits to the individuals involved. Thus, exploring fine-scale patterns of such social interactions within groups can help elucidate causes of group living, and can give insight into the causes of delayed dispersal. We studied affiliative social interactions (allopreening and “proximity”) of group members in the cooperatively breeding purple-crowned fairy-wren, Malurus coronatus, a species where subordinates may delay dispersal and assist dominant breeders. We investigated how the frequency of interactions between a focal subordinate and other group members (dominants and subordinates) was associated with their relatedness (kin, non-kin) and sex (same sex, opposite sex). Subsequently, we tested whether engaging in affiliative interactions was related to body condition of the focal subordinate. We found that affiliative interactions occurred only with kin or potential mates (unrelated, opposite sex). Thus, group members only affiliated when a social relationship offered potential indirect or direct fitness benefits. Subordinates that engaged in affiliative interactions had higher body condition, and this appeared not to be related to a trade-off with time available for foraging. Thus, the benefits of group living for subordinate purple-crowned fairy-wrens may be moderated by group composition, and an improvement of condition due to affiliation with kin and/or potential future mates on the territory may provide an incentive for subordinates to delay dispersal.