The thing is, Anne cheats throughout the story. Some people might argue that the "open" nature of the relationship doesn't allow for cheating, she can sleep with who she wants. I disagree. An open relationship has limits and rules. I also feel this isn't an open relationship. Those arguments aside, Anne cheats everytime she screws someone that the MC is not aware of or participating in. Her relationship with Ryan (unless you choose to fully support Ryan) and Dre certainly are out of bounds. The way she is with Troy, the doctor, the two guys... That is all in the realm of cheating. Then, of course, there is Walker (and I suspect, Troy, in the future).
My point is you do not have to follow the main storyline to get all of that. Choose no for Martin but play all you want with Ryan without the MC knowing. Anne will be be inappropriate with Dre if you choose that storyline. And so on.