Steve, if you honestly believe that your wife is involved in a homosexual affair... why do you want to stay married to her?

If she's gay... she's gay. That makes her an unsuitable candidate for heterosexual marriage in terms that are going to be meaningful to you.
I still think there's a possibility that she's gone middle-aged crazy and is acting out on resentments and perceived controls. But if that's not the case, you don't have a whole lot to work with here.
In either event, introducing some REALITY into the situation is probably going to be your best bet. Visualize what YOU would want in a divorce scenario, imagine your life five years from now... then see an attorney and start making it happen. Disregard what suits HER, and start suiting yourself. THAT's the reality of divorce.. when you look at your STBX and say, "Hey, we're not partner's anymore and I've got to start looking out for myself now."
Nothing like good old Mr. Reality to put things in perspective. So, you don't have to be a dick about it, all you have to do is be REAL. In fact, I think you should be as pleasant about it as possible. If you get a divorce, things are going to be different. You're going to be looking out for you and your kids. She won't be an integral part of
your little family anymore.
Giving her a peek through the window of divorce gives her an opportunity to back-peddle if that's not truly how she wants it to be.