I think you will do so much better keeping a level head. You have the evidence, keep it somewhere that she can not get it. I would expose fully to OM's wife. Not to cause her pain but keep her up to speed. She has some choices to make too.
Maybe you could make the couch up for her before she even gets home some night. That might shake her up a bit.
kat
Me-53(and learning!) S24, S21, D18, D17 Just keep swimming, Just keep swimming. Dory