I know both the DW and DH and I know for a fact he is cheating on her and has done previously.
So as not to drip feed I know for a fact because a friend of mine knows the current OW. I know a friend of the DH and he has told me about the excuses the DH made when he was seeing previous OW. So he had it from the horses mouth.
However, I won't tell the DW but I think she has a right to know.
A lot of posters say on threads like these they would rather know but I don't know that this DW would rather know. She might be one of those who would rather not know. So how can I tell her if I don't know if she would want to know or not. I am about as sure as I can be she doesn't know and that they don't have an open marriage etc.
I would also feel responsible for all the hurt caused if I told her something she might stay totally oblivious too. If she never finds out then she won't get hurt by it but if I tell her she does. They have kids as well.
So I know why I won't tell her. But when I see her and she speaks well of her DH I think he's a piece of shit and she has a right to know and make her own choice.