I would back away from contacting or even referring to OM - you are elevating him in importance when he isn't worth it. Besides, as much as I'm sure you can't standOM, HE is a symptom of the problem, NOT the problem.
Now, at the same time, I am NOT suggesting you back away from your boundary. And if she refuses to stay within that boundary (no contact with OM), YOU have to enforce it. You may not be able to force her to move out, but you sure as he11 can initiate the D proceeding. What's your alternative? She has made it clear she doesn't respect your boundary - she's testing you.
So, if you do not want to jump to the next level and file, tell her you have decided you will not live in a M where she cannot be faithful to you. And that you have decided you should both discuss how you will split up hte property, custody, etc. Make an appointment with a mediator. Just get the ball rolling. Unless you like how you feel, and where you are, right now.
