Well, welcome to the Staying & Improving board. We're down for the long haul here.
I really don't have much situation-specific advice for you, as I've never been in your shoes of trying to get a BPD mate to come back and stay... .(ahem, yet... .fingers crossed... .).
All I can off is to Read The Lessons:
https://bpdfamily.com/message_board/index.php?topic=56206.0And the new one specific to mates:
https://bpdfamily.com/message_board/index.php?topic=56303.0Both are deeply valuable, I return to re-read the Lessons all the friggin' time to keep some perspective and not get lost in the FOG (Fear, Obligation, Guilt) or to get wrapped up in the hopeless vicious circle of JADE (Justify, Argue, Defend, Explain).
Spend some time time here, and the biggest thing that jumps out is that You Are Not Alone. We're pretty much a bunch of people with the same problem: the ones we love have a serious disorder that has the effect of making love very difficult.
Hang in there man!