[I apologise in advance if this isn't the right sub to post  into]
I was in a relationship with someone who has BPD, and I didn't really know anything about the disorder during. She casually mentioned it over the course of our relationship. We had a lot of fights and misunderstandings which I tried to clarify with logic, but it didn't seem to work. Towards the end, it became unbearable where she would ask me to do certain things or act a certain way but get angry for listening to her. I was still pretty attached so I ended the relationship stating I'd like to be friends, even if that meant the occasional text or call once every few weeks.  We live in different cities so meeting was not going to be an issue. She agreed and understood that we weren't right for each other in that capacity. 

The months that followed were pretty painful because I tried to detach myself from her, and had to adjust to a new normal. She did the same and we became less toxic with each other. I was pretty happy that this was handled well by both of us. She came to meet me a few weeks after and tried to have sex but I stood my ground knowing it would probably ruin the new normal we had created. She didn't mind and we were completely fine. In the weeks that followed, she lost her temper with me a couple of times when she would randomly text me saying I was infuriating without a context, blaming it on the fact that I didn't get how her mind worked (due to the BPD). I didn't really respond to these and just stayed away because I really don't know how her BPD works and it also didn't matter now that we were over. I was sympathetic, don't get me wrong. But the more I tried to help, the more I seemed to be pissing her off.

[Fast forward a month] Recently she was going through a tough time with a move away from home and started talking to me more, and I replied whenever I could as casually as I would with anyone else. When she was nice to me, I responded with niceness too (wishing her luck for move related things). This went on for roughly two days before she sent me a long message telling me she can't do this (by this I mean be friends). She wasn't sure how to be around me and she needed space. I was obviously very confused because I thought I did give her space and every conversation we had with each other since was initiated by her. She explained that her mind was very sick and it didn't register me as a safe space for her anymore. She said she can't talk to me ever again, and needs to go back to the headspace she was in before she met me. I blocked her on all social media after that so that we don't come on each others feed or message. 

I broke up with her months ago, and the detachment became a lot easier last month. If the breakup already happened, I don't understand why this thing hurts so much. I've been researching BPD and how to deal with a breakup, and I see people suggesting not to take these things too seriously because BPD people are known to be volatile in the way they treat their loved ones. I can't help but take it personally though and I don't really know what to do. I read another point somewhere that's been disturbing me too, that BPD people break off from their SO's and are able to sort of erase their feelings for them as though they never happened. I wanted to verify if that was true. Could somebody please give me some advice on how to handle this emotionally? I'm having a very difficult time reconciling this entire situation and it's giving me anxiety. 