I'm sorry if this is the wrong place for this, but I thought I would talk to people who have experience with BPD. I was with this girl who has BPD for a few weeks and we had an intensely close and intimate relationship. I saw that there were too many issues to make it work between us, but I said that we could still be supportive people for each other while we figured shit out for ourselves. 

She met a new girl and instantly switched over to her. I can't be too angry since I didn't want a relationship, but it was like I became leftovers overnight. She got annoyed and short tempered with me, kept snapping on me and being prickly. It was like, I was an obstacle to her but also she didn't want to tell me. Finally I dragged it out of her. 

The second she told me she was ending our non-committal relationship, she got super, super happy. Her ending things because I didn't want to commit is one thing, but it very pretty painful to see her celebrating the end of what I thought was a very loving partnership. She knew this other girl for about four days at the time of ending things with me. They were fooling around and inseparable from day one. Although we had an open relationship, it was still upsetting that there was sexual overlap with a person she was romantically into. 

When I tried to talk to her about stuff, she just shut me down. Things went very badly with the other girl. Their relationship was so codependent it stressed her out, and now I'm suddenly back to being her FP. I'm so confused and want to be considerate of the fact she has BPD but the contrast is throwing me off and she cannot seem to wrap her head around why I am upset at all.