Therapist here. There's no winning even if they do get help. BPDs are the worst patients. >.>
100% agree with everything MusicalRose said.
I was trying to be positive as I know there are courses of behavioral therapy that are available in some bigger cities.
My experience has been with a co-worker who took me to court because I had firm work boundaries with her the she distorted beyond recognition. She convinced herself I was being racist, sexist and sexually harassing her. I complimented her on how nice she looked in yellow (she's chinese), she told me she is bi and as I am pan I talked with her about her feelings. I helped her find and apartment to rent as she had never lived away from home at age 34. Such as is the culture she came from. She asked me to tell her about living away from home and then said I was racist and controlling.
My "help" and friendship was bastardized beyond recognition by the time three years passed of court dates being moved because she had a sick note. I also miscarried during that time when the papers came to explain why I was being taken to court and what her documented evidence had said... Transcribed from recordings she had of our conversations. The whole time she came to my house to hang out and play with my son, went out for coffee after work to talk about her home struggle she was distorting everything that went on between us and writing it down or recording it. She wasn't diagnosed until after all this. I might of been able to avoid the pain more had I known her diagnosis.
I also have some experience from this last summer when my friend dumped his gf. You can read about it in my blog. I wrote about it lots there.
I worked on a mental health team, at an out reach program for the homeless, at a house for sex trade workers and at a needle exchange. I was a practicing art therapist at the time and was warned about several of the clients we served. I watch several good therapists burn out and leave due to their supporting and advocating for patience with personality disorders.
My personal take is to run the fuck away very fast. I have nothing left to give any more personally. I can see it coming a mile away now and turn and walk away immediately. I don't even want to watch others try as it drives me crazy to be anywhere near the drama that is caused.
I keep positive because there is always room for change and for certain situations to work out with the right fit of people. If you are emotionally and mentally healthy and have a life ahead of you that can be matched with someone else that is similar to you. GO! Just go to them. Don't waste your time on rationalizing and trying to figure out how to fix or trying to understand why or believing that the promises of working on it are true, because they just aren't at the end of the day. Calm, relaxed, everyday, stress free, drama free days are just never going to be the norm and unless you love that, don't stay. Whatever happens you'll be in it now and there will be no empathy for your part in the situation. Its all about them all the time and until the end and beyond. There might be moments of recognition that they got it all mised up, but the need for drama over takes.
Save yourself before you become bitter and untrusting of everyone like I am with most people now. Lol.
Sorry I sound so absolute here but fuck it. On this topic I have good reason to sound like that, hahaha. *sigh