Hi Rainy,

I am newly diagnosed with BPD and it floors me how I've treated others - through no fault of my own, however, it's up to me to figure some things out and to stop treating people like they are my own personal punching bags.
There are a lot of online support groups for family and friends of people with BPD. My search for a group of people with BPD lead me here - just last week! So, maybe check some of those out.
And I agree with everyone here that honest communication and boundaries are key to surviving your friendship. And more power to you for wanting to help - part of the problem is that those of us who suffer with BPD so want to have love in our lives but are so busy pushing everyone away that our fear of abandonment becomes a self fulfilling prophecy.

Good luck!