In their travels (handwave), Joe and Nicky have gained access to a ridiculously powerful aphrodisiac substance. Just a small amount turns a grown man into a helpless, pleading, begging, insatiably horny mess. When no one else is around they like to take turns dosing and fucking each other into oblivion.

Only thing is, that the effects take a while to build up. So for example Nicky will take a dose in the morning and spend the entire day getting slowly and steadily more hot and flushed and sensitive, and Joe quite purposely torments him by “accidentally” brushing over his ass or wandering around with his shirt off. Watching his husband’s self control gradually come apart until it finally breaks is as hot as the main event.