Firstly, thank you for responding to my thread the other day. Your words meant a lot to me.
As for your thread, as far as I know people with BPD tend to get involved with narcisstics... now I'm not saying your friends/partners are, but clearly they're very opinionated. You seemed to have answered your own question, in saying that you gravitate to these people because you don't have a strong sense of self. While this might be true to some extent, you might also be genuinely interested in the things they're interested in.
I have an idea and I'd like to know what you think... what do you think about getting a list of needs and also a list of values and start identifying what your needs and values are so you know what they are in a more concrete way BEFORE getting into a relationship with someone else? And revisting those needs and values list every so often as they may change over time.
I think this is something I need to do for myself actually. How about you?
I'm going to do an internet search for "list of needs" and one for "list of values" to help me get started.