I don't have that answer. Only your H can answer that, M. You can only make yourself better and hope that his infatuation with the OW runs it course. I have heard that most A partners are totally different than a person's spouse and that the Wayward spouse often settles "down" from the spouse when choosing an A partner.
I wish I had the magic pill or perfect answer to get you through this.
Oh...and yes, it's always possible that it could be a revenge thing; that's why it is important to act "as if" you will be happy without or with him. That way he gets the message that what he's doing is not having the effect on you that he had hoped.
But in the end you are DB'ing to make yourself stronger and at the same time, more attractive to him.