Ambivalent: Dotei wo Sutetara Shinu Sekai

A novel sexually transmitted disease is spreading throughout the world. Infection increases women's libido by several dozen fold but causes death in 99% of men. It's a world where "casual sex = death." The protagonist, Sadao Shindo, who has never experienced sex, vows not to have relations with anyone until a vaccine is developed, but he is assailed by the temptations of women...!