This is pleasure by Mary Gaitskill

Quin and Margot have been friends for more than twenty years. Quin is an extrovert and a sensualist who thrives on flirtation and ambiguity. He is at his happiest when encouraging intimate confidences from the women he meets. Always clear with him about the boundaries of their own relationship, until now Margot has looked on his behaviour with a mixture of ambivalence and affection. But when Quin’s actions are held up against a new light, and his life begins to unravel, Margot tries to work towards a deeper understanding of her friend, the damage he might have caused, and the loyalty he deserves.