It's highly debatable whether you can consider what Anne is doing is actually cheating, within the terms of their open relationship. Obviously, in the terms of the relationships of most normal people, it would be considered cheating. But those terms don't apply within their relationship, since Tony has effectively given his wife a free pass, to have sex with whoever she wants, whenever she wants ( and that includes his father, because when he finds out about it, he doesn't exactly get upset), and by the end of Chapter 14, she has effectively done the same thing for him.
Personally, I don't think faithfulness has any relevance in this game, since both Tony and Anne develop to the point where they are both incredibly blase about each others sexual adventures with other people. By the end of Chapter 14, neither of them are jealous in any way, of the other having sex with anybody. So I don't understand why it would be necessary to rewrite anything. Because regardless of what went before, they both end up in exactly the same place.
And to be quite honest those complaints about Anne's behaviour, were hopelessly hypocritical anyway, considering the MC repeatedly had sex behind her back himself, and never shared any of that with her ( at least over time she owned up to him about virtually everything). Why were those people so upset about Anne's behaviour, but apparently totally OK with the MC doing precisely the same thing and never coming clean about it ( until he had to in Chapter 14)?