While I agree with almost everything you've said, people who were assaulted 'lying' about cheating isn't that unusual. Particularly women are frequently faced with ideas that it's their fault for the assault or asked for it etc. Means sometimes the shame after the assault can lead you to feel like you've cheated, though total nonsense. Plus some partners/men etc think they have been cheated on, even if it was assault. Not saying that's what's happened here, I don't know, but it is possible.

In this situation though, regardless of 'truth', as you said, no trust left, and you can't have a relationship without trust.