CW: small mention of self harm

I don't feel like a person, just an empty shell with no consistent personality or emotions. When I'm alone and no one is around me, it feels like I stop existing. When I'm around people, I just *become* them and I take over their whole personality. When I'm alone, I don't have a personality, I just exist, waiting for someone to come around and give me a new personality to inherit. I'm so fucking sick of it. I want to be my own person, I want my own personality, I don't want to feel empty when I'm on my own. 

How can I fill this void? How can I start being my own person without relying on others to give me a sense of self? I don't enjoy anything when I'm alone, because "alone me" doesn't have any personality traits besides being a pwBPD. I just don't exist, don't move, don't do anything when I'm alone, I literally stop existing. It makes me extremely suicidal knowing that I'll never have a normal life, and that this is how it will always be for the rest of my days. I'm only 22 and I just don't see a future for me, I push everyone away anyway, and the people who I desperately want to keep in my life, are the ones who end up pushing me away because of my extreme moodswings, splitting, and obsessive behaviour. I just want to selfharm so badly again, but I've been clean for so long and don't want to relapse. I also really need to work on my Master's dissertation, but I just can't since I don't really care about it. The only reason I want to do well is because of the validation I get from others. But now I don't have "others" anymore, I also don't have a reason to continue working hard to get good grades. Please give me some advice on how to feel like I'm a person of my own.