She tells me how great the sex is with the OM. She tells me what they have and have not done.
Yeah, sounds like a real quality keeper there.
Sorry I can't be of more help. My suggestion would be to work on some good individual counseling to find out why you're still attracted to someone like this, and read the book "Co-Dependent No More." Perhaps I'm missing something here, but since your replies are so brief that's the way it looks to me.
You have a 13 year old and a 17 year old son, by my math. I would suggest to you that they are at VERY formative ages for how they relate to the opposite sex, and how they learn to draw (and lovingly enforce) boundaries in their relationships and in their lives. How would you counsel your oldest, say 10 years from now, and he came to you and presented the same situation as yours?
