You're looking for reason from a fogged-out, reason-less spouse, but I'll take a crack at it:
I think that the marital conditions that would make one partner look outside of the marriage to get their needs met -- whatever they are -- do lend themselves to repeated looking, so if it hadn't been this guy, it might've been another. HOWEVER, it's also true that wayward spouses almost always re-write marital history, to make it worse than it was, to justify their adultery.
Did she have legitimate, communicated marital complaints before her affair? Or just retroactively after it?
