Do BPDs have difficulty accepting help/support (or acknowledging that that they have received help/support) without feeling like they owe the person everything? And I don't mean in a "healthy," appreciative way ... .but in a very extreme way?
And if so, what is this attributable to?
My ex was on the dissociative spectrum: she had a "little girl" part of self, an older "teenage" part of self, an adult self, and probably a few others in the mix. Each would take the "lead" for different lengths of time.
I now understand that I became a caretaker when her "little girl" self took the lead. It's not a role I've played in any other relationship. Her "little girl" part of self wanted to be unconditionally loved and protected - she anxiously desired "safety" above all else. I believe we lasted as long as we did because I helped her feel safe.
Her "teenage" self was her part of self that was borderline. It was this "part of self" that I met - she pursued me, idealized me, was very sexual, impulsive, etc. Later in the r/s this part of self came back - angry, unhappy and avoidant. She complained that she felt controlled, talked down to, and wanted her freedom. Unfortunately, that "freedom" included sleeping with other people during our relationship.
Other times her "adult" part of self was in the lead and wanted to make our relationship work in a healthy way. It was this part of self that could admit that there was something wrong with the way she functioned in relationships. Her "little girl" self didn't really have the ability to analyze our relationship at all. Her "teenage" self blamed everything in the relationship on me.
To say that the way she switched to different parts of self was confusing to me would be the understatement of the millennia. I didn't really understand it all until months after the break up.
So, to answer your question: sometimes my ex was very grateful for the things I did for her, but at other times the things I did made her feel oppressed and controlled, while at other times she understood that, in an adult relationship, it was a "team" approach and I might contribute and help in some areas, while she would help and contribute in others, and it all worked together for the good of the "team." In the end, how she felt depended upon who was in the "lead." I finally came to understand that the real problem was that none of her "parts of self" communicated with one another very well, so I think her shifting feelings and beliefs were perplexing even to her.
I don't know if any of this is the case for your ex, however. I bounced back and forth between trying to figure out if she was "dissociative" or "BPD" until my therapist explained that it's not uncommon for only one "part of self" to be BPD. Many things began to fall into place for me after that. Nothing I read up to that point ever described someone in this way.
It's all very sad. I loved her very much but the infidelity broke my heart. It was the final straw for me, even though I didn't want it to be. It changed everything.