And, I don't mean win W back, I mean win in the sense of proving her "wrong."
Tell GF I suggested she dump you until you leave your (nonexistent) M behind you.
OR, try on this for size. MAYBE you are avoiding deeper connection/intimacy with GF by becoming (re)newly obsessed with XW. So, maybe this isn't about your R with XW at all. Maybe it is about YOU and your problems with really becoming involved with someone at a deep level because of your own fear of intimacy.
Hmmmmm... I'm thinking that sounds right.
But, either way, tell GF it's not doing anyone any good for her to be more into the R than she is. It keeps her unhappy and you stuck because you don't have to do any work to maintain that R. She needs to STEP AWAY FROM THE R.
Then maybe you can figure out what you want. And, if it is her, IF you are lucky, maybe she will still be open to an R with you.