Disclaimer: I have not officially been diagnosed with BPD, but my therapist has mentioned she notices a few characteristics.

I was in a relationship for about 2.5 years with a guy. I fell in love with him within the first few months and things were fantastic. Like any relationship, the honeymoon tapered off and things changed over time. I caught him in a lie regarding another female he had been involved with before me. I am not sure why he was not honest about it from the beginning as I would have been understanding, people are allowed to have friends of the opposite sex. The fact he hid it was the part that made me suspicious. I tried to break it off after this, but he came back groveling with flowers, chocolates etc...I was in a secure place until that happened. It caused a rift in the relationship and made me feel insecure. Throughout the relationship, I would often feel undesirable and worried that he would leave me..I am someone who already enjoys words of affirmation (my love language) but I did need reassurance and validation more often. He broke my trust. He was never one to open up about his feelings, so when I started to feel something was off or when wasn't treating me the same, I would try to discuss it. He stonewalled, or would get flooded and the discussions turned to arguments and would usually never get resolved. He didn't seem to care, and he never would take accountability for his actions. It got to a point where I found myself unable to handle the frustration and would start lashing out. I felt as if I was pouring myself out, and felt minimal effort in return. I should have left then, but I cared for him so deeply. I would get angry quickly after going over the same arguments and we'd get into screaming matches (me screaming, not him.) Around the holidays, things became pretty intense...I caught him in more lies. We fought for days...bad fights..I would break things, and felt unable to control my emotions. I am ashamed to admit this, but at one point I got so angry after catching him in another lie that I hit him. I have never done anything like that in my life and I profusely apologized. I feel horrible about it to this day. As this went on, instead of trying to work with me through it, to repair the damages of the lies, he shut down completely. He would often make comments that made me feel down, like a burden, an obligation. We had hours of long talks after that and I felt so much better. I finally felt mentally ready to give this another try with some boundaries. Well, like the flip of a switch, he cuts me off and says I am bad for his mental health. Naturally this upset me because he has done some emotionally damaging things to me as well. We both said we would forgive and move forward. Well the cutting out was short, about 5 days, lived as I was really struggling with the loss. He said he wanted to see me to a good place, and when he came back into my life, there was a sense of relief from the pain. I started to see a therapist more regularly to help with my depression/anxiety numerous times a week and our plan for the joint therapy stayed in place. For the most part things were good, little riffs here and there. We start becoming intimate again, and it's absolutely fantastic. Well...until I got in a car accident the other day, and asked him if I could stay at his place so he could monitor a concussion (he is an EMT). He gets all riled up, asking why it's always him....making me feel like a burden. Then the past few days, I just started feeling really low. I ask him to build me up, to bring positivity to the relationship. He says he will, and communicate better.
About a week and a half ago, he decided he can't do this anymore...AGAIN. We are talking normally, having a conversation and boom flips a switch..he feels like shit everyday, my problems have become his problems, he has to focus on him and cuts it off as he says.. Stops responding and everything. How he's so tired of it, that he wants peace. We were supposed to have a therapy session and he didn't show up. I'm feeling beyond hurt and blindsided. The fact he flip flops with the drop of a hat....literally mid conversation. For one, I have never felt so caught off guard. For two, we were sleeping together again, and I feel used. Three, we were literally practicing exercises with the therapist, and the sessions were going well. 
I can't help but blame my mental health isses for him pushing me away, for cutting me off. I'm feeling like such a burden, and that with how tough everything was this past year...maybe I am the problem. Maybe things would be easier if I wasn't around. I am feeling in that dark place, and having a difficult ime. I asked him to meet me one last time for closure, but he refused and now won't speak to me. Is there any coming back from this? I am feeling so much pain having him drop me, but also so much guilt and regret for how I acted. I've been hearing from mutual friends that I'm a "psychopath" and that I'm "crazy." To say I feel betrayed is an understatement, and I hate that he thinks so negatively of me. It has been a roller coaster and I truly don't know how to move on from this. Any advice would be received, as well as if you've had similar bad episodes like that. Am I truly that horrible of a person?.. because I sure am feeling that way.