I have severe manic depression and it's ruining relationships/friendships, how can I fix this?

I'm almost eighteen and never had a boyfriend. I've never been 'seeing' anyone longer than a month without them choosing another girl and recently I had been seeing someone for three months until they broke it to me a few hours ago that they didn't want to lead me on and that they didn't want a relationship. My manic depression gives me insane mood swings and crazy thoughts/antics which people don't seem to understand. I have a few close friends and a lot of people do like me in the beginning but once they learn how intense and messed up my mind is they back off. I don't want to be like this anymore, I'm in tears just typing this. Suicide is all that's on my mind right now because I can't live knowing I'm never good enough and too ****** up for anyone to want to KEEP me as their girl not just have a fling with me. It doesn't help that I have Borderline Personality Disorder, so my perspectives are distorted. My close friends say there is nothing wrong with me and that if they can't take me as being odd and messed up then they don't deserve me but it's too cliched and I can't believe it. Having such severe depression and BPD makes my loneliness worse, my heart is constantly in my stomach and I have that painful emptiness. I try and think positively yet it never works. I can't afford to see a shrink at $300 a pop for the best and even when I did they weren't much help. Any advice, anything, please. I can't live like this.