Yeah, you don't need to go that deep. Look through histories, myths, folklore from all around the world. Powerful men have mistresses. Regular men have mistresses. Powerful women go through several husbands. Regular women, too. The institution of marriage exists to counteract the natural human tendency to be "unfaithful". No one needs to make excuses, they need to accept the fact that this kind of thing happens and update their expectations.

I say this as someone who's family was torn apart by an affair, by a failure to update expectations. Well, that was the excuse; the issues were deeper, the affair was a focus-sink and an excuse not to address them. I wonder if that's the case here, too.