YOu're trying to confront him, TEACH him, land "truth darts," and more, all in one meeting.
SEPARATE.
This one should be only "I have decided that this isn't working for me. I will not live in an open marriage, and have you lie to me about it. I know all about you and (OW), and it's incredibly disrespectful, and I value myself too much to keep doing this. We both have some decisions to make, but make no mistake, if you don't end this thing, I will do what I need to do to protect myself, and to move on."
There'll be time later to land some good truth darts (and you've got a couple REAL GOOD ONES here!), I promise you.
I would do this privately, just the two of you -- don't involve any relatives.
