I’ve started looking for these kind of books after remembering a book I read a few years ago but I just can find it or remember the title. Maybe you know it.
Girl meets guy at a party/club and leaves with him.
She wakes up in a cage and guy, who drugged her, tells her he will let her out if she agrees to be with him and let him train her. Guy has a friend/assistant that helps the girl get ready for guy and befriend her.
At some point in the story he takes viagra because they have a long night of sex. Girl is almost raped by the guy’s rival/enemy?