There's a theory (supported by recycle behaviour), that they grieve in reverse!
And do indeed very much 'feel' the pain of a break up.
My understanding of grieving in reverse is... .Where you, myself & other non disordered thinkers & feelers grieve a loss straight away, they don't. They cover/suppress those feelings with distractions (usually but not always a replacement lover).
The distraction is novel, new, shiny etc. It works incredibly well, until it doesn't!
Then the lovesick feelings of loss, grief etc that we've faced months earlier surface in the BPD.
These feelings are as real to them in that moment as they were to us when we faced it. They are sincere. They are woefully sorry. They are ashamed. They are genuinely lovesick. It seems so real because it is real! It is really how they're feeling! IN THE MOMENT!
Recycle time?
Novelty wears off, go shopping for replacement again, exit again... .Round & round they and we go. Until we get off!
Theory works for me anyway.
Yah!... .Well isn't this sad poor little things. Well not for me there's just no way of changing the past or of any use at a point to understand his/her standing point. In the end, and with children involve they remain for ever who they are whatever if she realized it. The only important thing for me is accepting that from all it seems and all it is, she can't feel my pain because her emotional and logical interactions are just plain wronged! It did hurt to remind myself constantly of this, but if I would of kept feeling sorry for myself because she doesn't see nor feel , I would still be stuck in pain. Seeing things the way they are, not constantly trying to find odd, hidden explanations for the behavior they will always have is a huge step forward.
Yes they hurt us, did we try to get answers---yesss, did she willingly repeated the process? ----yes----- any different outcomes?------no--so accept it
Now if we look at own little pittifull self, did we willingly hurt ourself from denying our own beliefs and hoping in an all new end to the sick life story they offer---I did---
Now I can't dwell on hopes an understanding anymore but one's got to go through more less pain,understanding. Once you decide to accept all this, you realize how in the end unimportant what she/he felt but start to realize what YOU lured yourself in believing.