My internet research suggest that once the BPD splits you from black to white and their rage and impulsive behaviors resolve, they do realize and regret what they have done to their relationship. Is this what causes them to return and attempt to recycle a relationship that had value or meaning to them?
Honestly, the behavior is indecipherable. Sometimes they miss that you were any of these:
responsible, sensible, in control, loving, kind, gentle, giving, mature, helpful, abusive, argumentative, challenging, stable, unstable, sexual, asexual. charitable, poetic, straightforward, mysterious, emotional, unemotional, brotherly/sisterly, forgiving, unforgiving, insane, religious, atheist.
take your pick.
In truth, they regret the feelings of shame that they feel, any answer they give you as to why the returned is 98% likely to be a lie.
Mine told me the other day that she "knew" it was my birthday on Aug 23rd. Maybe she did. But I question as to whether that was truth. She came into my place of work (convenience store) on the 24th. Within a few hours she said happy birthday to me on facebook. However I noticed today that my birthday (without the year) is visible to anyone and everyone on fb, she could easily have come onto my fb after seeing me and realised that it was my birthday the day before and used it as an excuse. The fact she insists so much that she knew, tells me she's probably lying. After all, for a BPD another lie is just another minute on the clock at the office.
Would it be regret? hmm What do they regret? Hurting us? Or the hurting they feel?
I would say its a bad idea to project our own personality onto them, a BPD is literally always in 'survival mode', everything they do is to maintain an image, whether it be to be cool or to be kind. Some become suave and sophisticated seducers. Others become care-workers. I think they recycle simply to fill a gap, maybe they can't pull a guy/girl atm, maybe they remember something they liked about you and want to relive it for the excitement of it. I'm not being harsh about BPDs, I feel for them I really do. But from my own very very recent experience, it really is best to try and detach if you want to have any semblance of sanity and control in - or out of these relationships.