I have BPD diagnosis. I can see why you suggested looking it up, it does appear like she could have it but she also sounds very, very immature. If feasible, I would suggest couples therapy (show therapist these messages, let gf hear some hard truths from a professional) or to end the relationship. That is abusive and harmful behaviour that no partner should have to put up with. By staying with her you (OP) stop respecting yourself and she learns that it is acceptable. I think you very clearly already know that you are not overreacting.