I'm the One You Need

At the end of We Make Our Own Rules, Rob is reunited with Tina, his cuckoldress wife. He convinces her she's better off without Adam, her last lover. But he knows she'll never be satisfied with just him and will soon be on the hunt for a new stud. Meanwhile, Rob is confused. He still loves Tina, but also has strong feelings for Charlotte, the sexy young goth who befriended him when he ran out on Tina and Adam.
To make matters more complicated, Charlotte seems more interested in Tina. Adam introduced Tina to aspects of sado-masochism, which she's keen to explore in more depth. Charlotte has some experience of this and offers to take Rob and Tina to a BDSM club. Tina doesn't meet anyone there, but Charlotte encounters her abusive ex-girlfriend, Natalie. Despite Rob's protests, Charlotte goes off with her.
Rob and Tina run into their old friend, Nathan, when they're out for dinner one evening. Tina gets the idea that he might be the one to help her explore BDSM. He readily agrees and the three of them spend a weekend in a secluded cottage where Tina and Nathan can live out their fantasies. Rob is surprised and disconcerted by how much he's expected to join in. Once again, things get too much for him, and he goes home early.
Alone in the house, he realizes it's not Tina he misses, but Charlotte. He convinces himself that Charlotte wants to be free of Natalie, and puts into effect a plan to rescue her. Fortunately, she's grateful. The end of the book sees him wondering if he can start a new life with Charlotte.