How do I maintain relationships with moody people?

I am stumped as to the real me. My only longer-term relationships in life (platonic, romantic) have been with unstable, dramatic people. I feel like Joel in 'Eternal Sunshine of the Spotless Mind.' My last best friend had a BPD diagnosis. This is the kind of person I connect with and attract and I'm not sure how to deal with it. I've always been anxious, insecure, and a bit immature, causing me to be drawn to people that bring me out of my shell, but then again it chronically feels like it isn't working out in these situations - it'll get ugly over something petty and I hate it. I don't get offended because I am genuinely understanding, but then I feel like the put-downs are intentional at times. What am I supposed to learn from these relationships? How am I supposed to change or deal? Help.