I have/had/idk a BPD girlfriend. I caught her cheating recently with one of her online fans (she's an Internet personality). She admitted she was addicted to the attention and affection. 
I'd never heard of an FP but I guess that was me. We'd been together 6+ years, got a house, with plans of marriage, and kids. We'd also had minimal fights because I guess I managed her BPD behavior pretty well without even knowing much about it.
I wish(ed) we could be together forever, but I also draw a line at the way she'd treated me. It's hard for me to communicate my feelings without her cheating somehow being my fault. I try to reassure her that things would be resolved if she'd admit to her mistake(s) and work better to move forward. But she continues to lie and surround herself with toxic people who tell her what she wants to hear and influences her to engage in destructive behavior. I think most of these toxic people want her money, her fame, or to sleep with her. I'd hate to see her life get destroyed by these other people but I feel like I'm just watching her self destruct and I can't get through. I'd like for her to be safe whether or not we keep the relationship going. Is it even possible to warn her of what's happening? What's the best way to tell her? It seems like each day that goes by, these other people are creating a bigger divide between us.