Hi and welcome

It must be tough to go through a second relationship like that. A relationship with a person with BPD is kind of a special needs relationship.
This article has some useful info for making it sustainable.
It's good that you have boundaries. That's a great first step. Especially with pwBPD, it's important to voice your boundaries and stick to them. If you don't follow one of your boundaries, they'll notice and not take you as seriously. It is hard to lose someone you love, but there comes a point where suffering in an unjust relationship isn't worth it. Only you can decide when that is. You may have a natural tendency to be a caretaker as you've had two relationships with pwBPD. Stop Caretaking the Borderline or Narcissist is a book that helped me on this road to assert myself and shift my wife's and my relationship patterns to a healthier direction.
To answer your title question, no way to know for sure. Take a break for yourself then ask yourself, What do you want to do?