I just read this thread and damnit, it's been 15 years of your life Eiga Otoko.
It's just my opinion, but how about leaving behinde your exes for a while? I mean cut contact. Also I think you should take a break from considering girls a potential partner. Take a break. Go to Europe for example(just to stay in another continent), experience life in a new place, different culture etc.

Also if I understand correctly you tend to give girls alot from the beginning, basically you're very nice(a lot nice) from the very beginning. That isn't neccessarly a bad thing but it seems to be a bitch attractor. Maybe try not to rush( and I mean not to consider a potential partner every girl that you like), let the relationship sink(before the dating game begins), try to see and find the REAL personality and motivations behind a person before beginning to dedicate yourself to them.

I don't have the experience you have but looking from outside at your romantical situation the tips I wrote earlier seem the most suitable.

And remember, the important thing is not how much time it will take to happen, the important thing is if it will happen. And if you never give up, then the possibilities will keep living on.