Anonymous wrote:So not your place. Each person defines their marriage and values in their own way. It is between the wife and husband[b] - it is their vow, not yours.
No. Infidelity is not a marital matter "between the wife and husband" if one of those two people knows nothing about it. It can only be something "between" them if both of them are aware it exists.
Now you'll come back and say if the wife doesn't know, that's her fault for not paying attention to her marriage, or she ought to have read the signs, or whatever. Or you'll say she probably does know so OP should assume just that and not say a word.
People like you hide behind the idea of "That's private and privacy is sacred" when you actually just don't want to get involved. If you had a close friend whose spouse you saw out in the same circumstances OP describes, you wouldn't tell your friend, because you're such a strong supporter of privacy in marriage--? Doesn't it violate the privacy of a marriage if one spouse admits another person into it as a third party via an affair, and doesn't the cheated-on spouse have a right to know there's someone else in that picture?
Oh, here come the ever-wishful "Maybe it's an open marriage" posters, I'm sure. They and the "did you get fat" posters are reliable at turning up on every thread about infidelity.
OP, just find a way either to tell her or just to indicate he was out with another woman so she can interpret that however she chooses. If she ignores it, fine. If she is OK with it, fine. But you'll at least have given her a shot at deciding for herself what she wants to do, or not do, with that information.