Bath Haus by PJ Vernon

Oliver Park, a young recovering addict from Indiana, finally has everything he ever wanted: sobriety and a loving, wealthy partner in Nathan, a prominent DC trauma surgeon. Despite their difference in age and disparate backgrounds, they’ve made a perfect life together. With everything to lose, Oliver shouldn’t be visiting Haus, a gay bathhouse. But through the entrance, he goes, and it’s a line crossed. Inside, he follows a man into a private room, and it’s the final line. Whatever happens next, Nathan can never know. But then, everything goes wrong, terribly wrong, and Oliver barely escapes with his life.

He races home in full-blown terror as the hand-shaped bruise grows dark on his neck. The truth will destroy Nathan and everything they have together, so Oliver does the thing he used to do so well: he lies.