My guess is, long distance relationships are extremely difficult. No matter if you have BPD or not. My guess is, is that you pick the wrong partners because (yes this psycho babble) you're not ready for it. Long distance and age difference are two complicated things (especially if you're young). The best way now, especially since he's not 'reciprocating your love', is either to confront him about it. Tell him what you need, if he doesn't agree, well.. then you have your answer.

I do agree, as a BPD I tend to make dumb choices. I've never been in a relationship though. I've fallen in love, multiple times, but the thought of actually dating that person, kind of freaks me out.
To be very honest, I feel very uncomfortable around single guys, once I know they're in a relationship I tend to loosen up a little bit and am finally able to talk to them. I guess then I know they're not interested.
Anyway, I believe that this is different per person, and has very little to do with your disorder.
Best of luck!