What do I do about this g/f situation?

A while back the love of my life dumped me. There were a lot of reasons why, but suffice to say it wasn’t working out for reasons beyond our control. Shortly thereafter I found myself dating around, and one of the supposed flings ended up turning into the relationship I’ve now been in for a while. I never truly got 100% over my X, but I moved on and became happy with my new g/f… even reaching the point that I legitimately began looking at engagement rings.

Well of late things are not as rosy as getting married. The relationship has soured significantly. I don’t know that it’s beyond saving, but it’s become very difficult and our troubles are constantly on my mind. In the midst of this trouble, the X g/f (who several months back found herself single again) is talking to me and basically implies/tells me that she wants to be with me again and misses me.

With things as sour as they are right now in my relationship, and my feelings for the X never really fully dissipated, I find myself torn on what to do. I had made the decision I would try to sort things out with my g/f, but every time there’s a fight it’s harder to follow through on that. I have no idea if a new relationship with the X would even work, but the mere prospect of it, when faced with my current situation, sounds marvelous.

I’m faced with a scenario where I could be seeing my X pretty soon, and the prospect of that even being a possibility frightens me, because I’m not sure I could control myself. I’m not sure I want or SHOULD control myself even if given the opportunity.

What do I do?