Could just be me, but it'd never been allow to fester that long as I'm not one to sit and become embittered. If I see a problem, I'll say what I see/feel. Not rudely, I do try to be tactful, empathetic, and caring with people I love. If they are not willing to work on it, or flat our refuse, there's a much easier resolution than cheating. That's a hard red line I'd never cross, no matter the situation.
Had he stood up, much earlier, and said something things could have very easily played out differently or the same. At least he could have walked away with a clean conscience.