Welcome to the family, Afloat!
You've landed in a safe place full of people who understand what you're going through. We all know that combination of relief and fear (even horror?) that comes with "discovering" BPD. Definitely been there myself.
I hope, when you feel up to it, you'll share a bit more about your relationship. What sorts of behaviors does he exhibit? What are some primary problem areas?
The more we know, the better we'll be able to advise you and point you towards helpful tools -- if that's what you want. If you just want to vent, we're here for that, too!
Again, welcome!