As I'm sure you can easily tell from my waffling throughout the situation, I am having a very hard time contemplating cutting off all communication, or even confronting her in such a black-and-white way as to tell her that I'll have nothing to do with her life as long as OM is in the picture... It seems like an ultimatum to me, something I know that she never responds well to...
I would encourage you to reach out to Denver2010, and to read his sitch. There is a way to balance this, and he did it extremely well.
I will, however, say that I think (like a lot of people) you are having a difficult time understanding the difference between an ULTIMATUM, and a BOUNDARY. Rather than try to give you my own take on it, I will copy and paste a recent post from a friend of mine, who illustrated it far better than I think I've ever seen (just change the gender to fit your sitch:
Think about boundaries like this:
Boundaries are not about controlling the other person, because boundaries are about drawing "circles" around *you* and determining what you will and won't allow inside that circle.
Your WxH can do whatever he wants OUTSIDE that circle. You are not telling him what to do.
But you will only let into that circle people who treat you with respect.
He's free to go on treating you with disrespect, but you won't know about it because he'll be outside your circle. He's free to go on and draw his own boundaries of no expectations and no responsibilities, outside your circle.
He can do WHATEVER he wants. He's a free person, free to make WHATEVER choices he wants.
BUT SO ARE YOU, and you are free to choose who to allow within your circle.
That's all. Not about trying to control him at all. Tell him he's totally free. He has the WHOLE WORLD, outside your circle, to go and do whatever he wants.
If he's saying you have to let him into your circle no matter what, then THAT is about HIM controlling YOU.
