This post saddened me. I wish I was there to give you a hug and tell you how decent and good a man you are.
I think detaching and separating are not too different.
What has helped me is Frank_D's approach which is not to try to pretend that what she is doing is OK or to pretend you are "OK" with it, but to look at my wife in the middle of a MLC and an affair and realize, for lack of a better term, she's nuts. She needs help. Hopefully her real self, including her conscience, will emerge from the endorphin and emotional fog. Maybe it will, maybe it won't. And if she chooses to remain nuts for the rest of her life, so be it, I'll not be part of that life. Frank's approach was to "smile and wave."
I think, perhaps, you might want to do some hard thinking and come up with a plan. What if she gets married? Where do you draw the line?
I suppose the cliche thing to say is go sit with God. Tell him exactly how you feel, even tell him how awfully you think he's running the part of the universe you happen to be living in. Be brutally honest with him. Ask him to change you. Ask him to change your wife. Ask for a miracle. Then tell him whatever happens, you will hold him personally responsible for it, since he does rule the cosmos. But, since he's God, you will trust him with your life, your wife and your children. You may not like his decision, but, you will trust that because he loves you beyond imaginnig, that even the difficult things that come from his hand will refine you into gold.
Having given you spiritual castor oil, may I also say, there's always hope.
