I don't think it's necessarily a bipolar thing. People just suck at being friends a LOT of the time. You're lucky if you can say you have more than one person other than family that you can count on, in my experience.

I know that I can be a rather needy friend from time to time (I often need someone to talk to when I'm feeling anxious), so I acknowledge that I may have chased some people away. But I am a true blue friend, very loyal, and I am there for others when they need me, too. When you find the people that you really click with that can also be reliable, hang onto them with all your might!

If it makes you feel better, it was probably nothing personal. When people are flaky, that's just who they are: a flake. I try to remind myself not to take anything personally, too. Check out the book The Four Agreements by Don Miguel Ruiz. He teaches about not taking anything personally and it really helps in relationships. He has another follow-up book, The Mastery of Love. I recommend both of them. In fact, I need to re-read them myself because they are so full of wisdom.