I can relate to a lot of what you've said about feeling you lack an identity or that your identity is solidified through other people. I also can relate to having done the "mimicking" thing since childhood. I have always thought of it as being a chameleon. I have made myself like things I really didn't like or even abandon things I did like for the sake of being like the person I admired at the time (and god forbid our friendship breaks apart due to lack of common interest). Same goes for behavior, like their tone of voice, dress style etc.

From what you've said, your relationships seem pretty unstable to me, notably the "I admire them at first but if they disappoint me then I start hating them." My psychiatrist told me this is putting people on a pedestal, and is common in BPD.

I also relate to not really feeling emotionally close/able to open up much to your parents, but for me it's a bit different because I did experience family related trauma in my childhood. I also started becoming symptomatic as a teenager, due to both life events and the nature of this disorder (I was told it's common for BPD to begin showing itself in adolescence).

Whether or not you have BPD I cannot say, but did you mention these specific things to a psychiatrist, or did you begin realizing more about these struggles after they told you that you have BPD traits? I'm sorry things are hard for you.