It's difficult, I know... it sucks. But I think it would help if you tried taking a step back from all of this. Both of your friends have issues, issues which you cannot fix. You are only responsible for yourself, and your well-being. All you can do is be there for them, without trying to pressure them into engaging with you. Will they reciprocate? I wouldn't count on it. Sadly, psychological/mental issues can push someone towards becoming quite self-absorbed. People think and handle situations in different ways. I've had friends who have become so absorbed in their own problems, that they completely forget about everyone else. At that point I'm not sure there's a whole lot you can do. It's not necessarily their fault I guess, but it's not yours either. Do you have any close friends who also have BPD that you talk to? Maybe you would find that beneficial.

I've heard some positive things about DBT. I started reading through a workbook I found online, but never got around to finishing it. I hope it helps you overcome some of the difficulties you're going through. At least to think about them in a different way. Because at the end of the day, you can't change other people, but you can change the affect they have on you.

I'm not sure what else to say, and I don't want to say something wrong. It seems like you're trying your best to overcome and make sense of the situation you find yourself in, which is a REALLY good sign. Hang on in there and don't give up!