Been looking at this forum to help quell any doubts I ever had about what the hell I was going through.
I am going through a similar situation to all of you. 4 months ago me and the ex parted ways. She knew I was miserable and being in a relationship with me made her miserable, but here's the thing.. I didn't do anything to make her feel miserable. We were together for over 3 years and for the last year I was emotionally checked out due to all of the shlt I had to deal with on a day to day basis.
My ex is clinically diagnosed with depression and has a family history of mental illness. After reading some of the clinical signs of BPD I am 100% convinced that she is one of these people. Throughout the entirety of our relationship, I was fundamentally and mentally the same person, all of the time. I am very comfortable with who I am and couldn't give a fvck what anyone thinks of me, positive or negative.
Now, while I was the same person all along who she 'fell in love' with, she was not. Sure, she had the same personality, voice, physical features, you name it, but what changed was her mentality. Everything that we had set the foundation on for our relationship to succeed had suddenly been torn down and for reasons that were beyond my control. One big example was a loss in trust. I had never thought about, or acted on any urge I had to sleep with someone else. In the beginning she understood this, and had all of the faith in the world that I would make the right decision when put in a situation like that, and I always did.. We were in college so these situations happened frequently.. But eventually that changed, and for no reason what so ever. Did I make other mistakes? Sure... No one is perfect, but when someone with BPD acts on their raw emotion, there is no merit to their thought processes, and therefore my credibility with her slowly declined, for very very trivial reasons.
Soon enough everything became a game. The 'say one thing but want another' game is another hallmark symptom of this illness due to their uncanny need for validation. And she took it to extremes with me at some points in time. Soon after that, her thoughts became delusional, to a point where I wasn't allowed to do things on my own without her. She would cry and always tell me that she never thought we'd make it together, and tell me not to fvck other women even though she should have had absolutely no reason not to trust me. She would have anxiety attacks and cry all day when she had too many things due in school. I stayed up until 5 am one morning writing the 2nd half of her 50 page paper for her, just so she could sleep and not worry. Which leads me to my last, and final step in a BPD relationship. This is, you can do no right.
Yeah, that night I spent up, never mattered in the end. It truly was a waste of my time. Was she grateful at first? Sure.. but it lasted a whole 24 hours before it was thrown to the wayside. For BPD's it's a 'what more can you do to prove your love to me' type thing, all of the time. Any mistake I ever made was always brought to the forefront, no matter how minor. I got better at the end with not dealing with her shlt and just walking away, but I my phone would always blow up minutes later with calls about how she was sooooo sorry and that she's fvcked up. Don't fall for it guys, because the next thing you do wrong, no matter how minuscule, will be your undoing, over and over again.
It's been 4 months. I was the happiest man alive for the first 2 months of our breakup.. She was never on my mind. About 3 months in, her mental grasp began to reel me in and it has been a bit troublesome ever since. Best thing you can do, find someone else, someone who is capable of conducting a normal relationship. I have been seeing another woman for 3 months now and every time I am with her, she makes me feel like a king, the way I should have been treated, and it makes me that much more willing to treat her like a queen. It may not be as emotionally deep as the bond with your ex but remember that doing you and not being afraid to show off how happy and satisfied you are is another step to making your ex regret anything she ever did to you. Karma will come around, just be patient and have faith that things will work out.

I am running 12 days NC and will keep counting with everyone.