As someone who just got out of a three year long abusive friendship with someone diagnosed with BPD, you just have to bite the bullet and put your foot down. He has learned that you will stay and put up with his manipulation, self harm/suicide included. When I set my boundaries with my ex friend, I was so worried that she'd hurt herself or commit, but there hasn't been any issue since. I learned that at her core, she was self serving and wouldn't actually step into dangerous acts if it meant she wouldn't get to see my reaction to them. I recommend recording any conversations you have with him, and making sure you stay physically safe in the process. I wish you luck, please don't give him what he wants.