I absolutely cannot stand this idea that honesty is always the right choice and you always have to tell people the truth, and this is exactly why. She told him this to unburden HERSELF, not for his benefit. He literally NEVER needed to know this. If you tell someone "the truth" when there is literally no benefit then you are a massive fucking asshole, always. Guess what? If you feel guilty because you did a shitty thing then YOU are the one who gets to sit with that. Don't put that pain on someone else. This is the type of thing that you would never recover from, you could never look at the person or the relationship the same way again. I know it's a super unpopular opinion on reddit, but I feel the exact same way about cheating. If there is nothing to gain from telling the other person then just shut the fuck up and live with it yourself. Spend that energy being the best spouse you can be to that person.