Your question is a bit vague so that's why it's hard to answer.
If she is talking about leaving or planning to leave - or senses you might leave - then it's possible she might feel she needs to abandon you before you can abandon her. If that makes any sense. Remember, BPD is a mental disorder and a lot of it doesn't make normal "common sense".
She has more family issues than I do, but she will never talk about them and only talk about mine.
My ex was that way too. It's part of the typical "Denial", also known as Guilting, Blaming or Blame Shifting.
If joint or family counseling isn't working, it may be that you each should have separate counselors and then after some sessions with progress you can try joint counseling again?
You don't have children together? Best to keep it that way, at least until you know whether things are getting better. I learned the hard way that having children does not resolve deep relationship issues and actually can make things even worse. And vastly more complicated with custody and parenting issues added to the mix if the relationship does end.
My story is a common one, shades of the frog in the cooking pot analogy. A frog dropped into a pot of hot water will jump out but if the water is gradually warmed it will stay and get cooked.
I stayed when my ex started having work issues with her bosses and coworkers. I stayed when she started criticizing our friends until they were alienated. I stayed when she started isolating us from my family. (She already avoided most in her family.) I stayed... until she started looking at me sideways as though I was abusing our preschooler. I finally realized nothing I did was improving things and so the actions I took (calling police when DV was looming) ended up with us separated and then divorced. I look back and accept there was nothing I could have realistically done that would have fixed the increasing conflict. It was her perceptions and behaviors that she refused to change. I had to stop being the appeasing fixer or apologizer and set some boundaries.
Boundaries were not for her, she never accepted them anyway since she always followed her moods of the moment.
Boundaries were for me. It took me a while here before I learned what that meant. "If you do or don't do ___
then I will do or not do ___." That may sound confusing but here's an example... "If you rant or rage then I will give you space, leave and go to a park, movie or restaurant until you have calmed down." Of course that particular example might not work if she's ranting in a late night "we will fix this tonight" interrogation, but you get the idea.
