Despite recent advances in research with gay male couples, less data exists about men who have had UAI within and outside of their HIV-negative seroconcordant relationship. Multilevel modeling with dyadic data from 142 couples was used to identify the characteristics associated with men who have had UAI with both their main partner and a casual MSM partner within the same timeframe. Analyses revealed that men were more likely to have had UAI within and outside of their relationship if they perceived their main partner has had a recent HIV test. Men were less likely to have had UAI within and outside of their relationship if they valued their sexual agreement and reported having a sexual agreement that does not allow sex outside of their relationship. Research with a more diverse sample of couples is warranted. Future interventions must consider the complexity of relationships and sexual behaviors among gay male couples.