Marriage, as a microcosm of society, involves the moral dilemmas of conflicting rights, competing claims, and responsibility for decisions. This study focused on the moral development of the individual-in-relationship using commitment and happiness as the common ground. The purposes of this study were (a) to describe justice reasoning and responsibility reasoning of individuals in long-term marriages and (b) to assess the relationship of justice and responsibility reasoning to commitment and perceived happiness. Separate in-depth interviews were conducted with 30 individuals in 15 long-term marriages. Data collected were responses to three hypothetical dilemmas, four real-life dilemmas, and questions on commitment and happiness