Sara, first of all my heart goes out to you as I was in the same situation many years ago with my wife. In my case, I elected to stop any and all CDing to save my marriage. A couple of things that made me make that decision, was the fear of losing the woman I loved, and the fear of being alone possibly for the rest of my life as I am not the kind of guy who easily hooks up with women. Also the fact that she might out me to my 2 children and my family, that could have put me in a situation where thinking of ending my life would be the only answer. This was just me, you might be more able to cope with the break up if you decide that is the route you are going to go.
As others have mentioned, counseling for the both of you sounds like good advise. But the counseling would have to be with someone who is familiar with GD and CDing.
Of course we are all different, but even tho I held the marriage intact, I was generally a miserable person for the remainder of the marriage until my wife passed away. Then all the flood gates opened and now I not only have been crossdressing, but I have full blown GID. The envy I have of women is making me depressed.
So not to keep rambling on, just wanted to give you some food for thought since I was in the same situation. Unfortunately, no easy answers. But if you really love your wife even tho she is giving this ultimatum, counseling is the way to go, and at least that should show if your wife is actually looking for a way out.
Wishing you the best during this trying time, and hope you do find some happiness in however things turn out.
Hugs, Tina