uhh, if I read correctly, "X1" is gone again... and "X2" is still around... so it seems to me you have a choice of either staying with a girl that you are at least comfortable with, or obsessing over a girl that's too far away to do anything about. Chances are, she's living a life of her own and quite possibly seeing people and not thinking twice about it.
So... the question, to me, looks like "Do I dump 'X2' and tell her it's because of 'X1'?" or "Do I just stay with the relationship with 'X2' that I'm in and hope I remember why I was in it in the first place?"
To put your analogy into better light...
Do you stay at a job that makes you financially secure, regardless of what it is, or do you quit and sit around watching TV all day in your underwear hoping that on a strange twist of fate, another job will open up to you and only you?