I think that, just like each person is different, so are relationships. The behaviors that are part of BPD are common, but the reasons for them are personal/individual.

What about seeing a therapist, who could not only help with your relationship but also with help your gf to feel better and understand herself better? You sound like a wonderfully caring, kind, and supportive person and she's fortunate to be in a relationship with you. I especially like that you are not willing to be treated badly. Good for you! Setting that boundary is important for both of you!