After a BPD leaves there old partner they still have fears of abandonment by that partner. They may have a new lover who will be there new knight in shining armour but they still have a deep attachment to there past partner and fear there abandonment. At first brush, this seems to be contradictory because as soon as they leave the former partner they demonize him as completely black and evil. However this is only on the surface. At a subconscious level they still have deep attachment to the previous partner they left. Hence they still fear the previous partners abandonment even AFTER that partner has left there lives and a new partner has entered. This is because the BPD's emotions are immature and leads them to want to recycle the previous relationship to make them erase the empty feeling they have inside of themselves. I know this does not seem logical but this is how the warped thinking process of a BPD person functions.
I have encountered this is diagnosed and undiagnosed potential pwBPD. One was a friend who told me out-right that she didn't love her ex (who was in love with her), but wanted to keep him dangling in order to feel wanted. It disgusted me to the core, especially when she tried to come onto me! I'll leave it at saying I no longer speak to her.
The second, of course, is an undiagnosed ex. And though I've understood what she's doing in the past, I've allowed myself to be scuppered by it on multiple occasions.
Without my validation she feared that I was gone for good and the issues of abandonment would start all over for her until she could overcome them for good (if ever). This is why there is so much recyclnig with BPD's after they have found a new partner and still gravitate to the old partner.
This is what always concerned and ravaged me within; knowing that^ possibility. Not because she tried (and failed) to keep me contained in a little box post-split, but the high possibility that every boyfriend I've seen her run through in the wake of our relationship is STILL orbiting her, and she's keeping them in orbit. I cannot stand this idea.
Knowing of the possibility, I've asked her whether any of her exes are around. She denies they are, of course. Bar one (the one she left me for) who turns up every now and then in attempts to ellicit for sex, she claims I'm the only one who managed to have "staying power". I'm not so sure about that!
The amount of feelings and fear of abandonment by the BPD towards there ex depends on the amount of attachment they have. If the relationship was very long and deep (such as our 14 years together or a mother/child relationship) it could be a lifetime. If it was shorter or had less intensity it could be far less. When you add things like children into the equation (I have full custody of ours and she cannot see them unsupervised) this fear of abandonment can be substantial. Things like alcoholism / drug addition / sex addiction only exasperate the situation because they significantly impact the BPD's impulsiveness / recklessness and open a whole set of issues
I feel for you. Your relationship is far more entrenched than mine. Mine is highly sexual. She actually -encouraged- to watch porn. But this isn't my thread, so I won't go into it.