I'll start by saying I empathize with your position. It's hard to know a lover has gone back to an x. Honestly, I believe that there is no way for anyone to be able to tell you if he's coming back. No one knows better than you how strong the bond is between you and how strong the old flame was in his life.
I've learned in my relationships to always look at myself and give sincere apologies when I feel I've made mistakes. Perhaps you could do the same if you feel it is warranted.
Keep in mind that even if you look at yourself and apologize for your half he may not come back. In that case, I hope that you'll take comfort in knowing you did all that you could do and you will have that experience to make wiser decisions in the future. Regardless of whether or not he accepts, you do still have the good memories of what once was. The fact is that all love stories come to an end at some point.
Truly, if you are meant to be together you will be. In my experience, I decided to let the guy go and move on with my life (after two weeks of pathetic sobbing and feeling sorry for myself) . As it turned out, the cliche "If you love something, let it go free..." worked as it says. He came back after a month knowing he made a mistake and the rest is history. We made a beautiful son together and even though we are not together any more, I am grateful for having him in my life at all.
Good luck to you...