Wishful Thinking,
I'm so sorry to hear what you are going through... . but it does sound like you are learning. Sometimes lessons nudge you. Sometimes they kick you in the ass so hard you skid 20 feet on your face afterwords. Sigh.
One thing you have mentioned twice is him saying "It is better for you if he leaves you now." I heard some things like that from my wife, and had a different reaction than you did.
I was !@#$!@# PISSED! It is NOT her place to tell me what is better for me. That is my job, and I may not be doing it well, but she sure as heck isn't going to be able to tell me that.
You own your feelings. He owns his. It is his job to say that he wants to leave you. It is your job to say that you want to leave him. That is how adults should behave.
Of course, he has BPD, and isn't acting like an adult. But here is one thing to remember--just because he says something like that, you don't need to believe that it is true for a second. Yes, believe that he means it (at least for the moment), but that doesn't make it your truth.
This is one more way of taking back your own life. Doing it will help you. I suspect it will make things better for your H as well, although you will get lots of kicking and screaming over it.
Keep your resolve, and keep working on yourself!