They're still a minor living with shitty parents so they can't seek a diagnosis yet, but they exhibit symptoms and have had experiences that often lead to developing it. 

I still need to do more research on it, and I'm going to, but I know about it in general. And something I'm aware of is when someone latches onto someone else as a favorite person. I think that's the term anyway. Thats who their partner was to them. It was unhealthy for the most part with them both being overly dependent on one another, but it got a lot rockier a while back and they eventually broke up about a couple months ago. 

I'm trying my best to be there for them. No matter what I'm always going to try to help and listen to them when they need me to. But I feel awful because between them having bpd and severe trust issues I just dont know what I can say to help. Maybe theres nothing I can say that will really mean anything to them. 

But if anyone can give me any advice on how to be as supportive as I can, or how I could help them trust me more, please let me know. I love them a lot and seeing them suffer is just awful. I'm going to try to do more research myself in the meantime, any comments are appreciated.