 This is going to be more of a rant, but I'd also like advice from others that have/had friends that have BPD/BPD criteria.   
I met a new friend at a new school program that I just started. We became friends instantly and she became suddenly very close to me. To the point of being physically close to me too. Nothing inappropriate, but if she wasn't in a relationship already I would think she'd want to be more than friends. And I am in a relationship too. She would always text me, even when she was with other friends/her bf. She shared everything with me, to the point of being dependent on me.   
I have had verbally abusive friends in the past. I'm going to say now that I am NOT trying to diagnose anyone, just what I have observed and studied. After studying abnormal psychology, I realized another friendship that ended may be because she had narcissistic personality disorder. So I was soon aware that this new friend was showing a lot of red flags. She claimed she was "broken" and I started feeling like I was walking on eggshells as anything I said could possibly trigger her and she would get easily stressed and verbally aggressive. What she thought mattered only. I was always wrong in her eyes. I think she was gaslighting me too. And I could never offer advice without her getting defensive. I am not perfect and I am sure I was to blame for some things. But eventually, I became very emotionally upset by her outbursts so I had a talk with her. I told her what I was having an issue with and how I felt. I tried being nice and not blaming. She understood, saying others have expressed the same concerns, and it all seemed alright. Things were ok at first until she slowly started distancing herself. And suddenly, she would barely text me, never wanted to even touch me, and would barely talk to me. I tried hanging out with her. I tried talking to her about what is wrong, but all she said was she's like this in relationships and we are both busy so it's natural to become distant. But I know it's not.   
I was very emotionally distressed because of this, as I was living alone in a new place for the first time and had no one else besides family back home. I was being rejected and distanced by someone who I had thought was almost my sister! During and after the holidays, I came to terms that I wasn't going to be able to repair our relationship. I still tried reaching out, talking during classes, but she would leave the moment she could. Any plans to hang out never happened. Then, we wrote a paper on BPD - a topic that SHE choose. And I soon realized she had many of the criteria for BPD. It was almost too accurate, but of course I have no idea if she does and she would explode at me if I try to talk to her about it. While writing this paper, she was constantly defensive at everything I said and impatient. It was like I did nothing right, that I was incompetent. I had severe anxiety through this whole process because of how hard it was working with her, how uncooperative she could be. I won't go into more details, because I'm afraid she'll somehow find this and get mad at me.   
Now it's like we are barely acquaintances. Strangers are more friendly than she is towards me now. I try to accept it but it hurts knowing how close we were and now she barely looks at me. It fucking hurts. And I don't know if I did or say something to cause this. If she does have BPD than it could not be my fault at all. My "discussion" with her does not seem like what caused it, but maybe it started the distancing process.   
Now, I just want to know how I move forward from here. What I would like to know is how other's coped with negative experiences with friends that had BPD. I know she's aware of herself but doesn't (or can't?) change or better herself, so I don't see how I can help her, or if she even wants it. How can I process the emotional distress I have been through and accept what has happened? I'm not saying I'm the victim here, but what I've experienced is also valid. I have mental illnesses myself and can empathize with the difficulties. So any advice would be nice, or if other's can share their story.   


TLDR: new friend became really close at the beginning, became verbally abusive and gaslighting me, when I spoke out she became distant and cold. Feel used and manipulated