Welcome to the site and so sorry to hear what you're going through. We understand totally because BPD runs like a pre-written script and all here have experienced exactly what you're going through; it's truly devastating to see someone change from the person you thought they were into a total uncaring stranger.
Since this post she has since gotten into a new relationship with a friend I had been concerned about just 15days after ending it with me. I will never understand how she ca. Hurt me this way. Will she ever return to me.
As has been previously said, this is standard behaviour for someone with BPD as they don't want to be alone and will rapidly jump - or 'monkey branch' as it's known - to others in their quest to find what they want emotionally. The problem is always that they never know what they want as their emotional needs change from one moment to the next; they're chasing the impossible.
The ony consolation is that she will inevitably treat her new partner the same way she's treated you. After the initial 'newness' wears off, she will see his flaws - whether real or imagined - and he will be treated exactly as you were. BPD is a repeating, self-destructve cycle which, without professional treatment and the willingness to follow it through, she will never be able to break.
As Foreverdad said 'the past is likely to predict the future' and this is 100% correct, as we've all found. She may well return in future - she seems to be keeping some communication going with you, but then BPD's will always try to keep people as options; a backup if all else fails, so be careful what you read into it.
The main question you need to ask yourself is 'Could I put up with this happening all the time, the constant cycle of love and hate?' 'Are the good times worth enduring the bad times?'The mental strain of a BPD relationship is definitely the worst I've ever been through and I'm sure most here would agree it's been their worst life experience too.
We're all with you, whatever you decide.