This chapter asks what kind of sexual desires and capacities are produced by heterosexual masculinities and what the consequences are for affective health in relationships. I define sexuality as an affective flow within assemblages of bodies, places, commodities, and ideas, as well as the capacities produced in bodies by this flow. Through qualitative interviews and ethnographic observations across ethnic and racial boundaries, the qualitative ethnographic case histories illustrate how desire and heterosexuality potentially unsettled assemblages of masculinity in South Africa. In this context, dominant gender practices – the performance of masculinity – could not fully explain desire. In the postapartheid city, however, affective flows led to new challenges for sexual and reproductive health. Customary law and ‘tradition’ as well as the neoliberal ideal of becoming ‘self-made’ captured Black, Colored, and White men’s desire in different ways and went along with relationship conflicts. Men felt disempowered in regard to sexual and reproductive decision-making. This contrasted with public health research and campaigns that emphasized men’s power, particularly in regard to HIV transmission and women’s vulnerability to HIV/AIDS.