Dx. I know what you mean...
I've been where you are...
For some reason people like that are the ones that I tend to care the most about, before I even find out that something like that is going on with them.
The best thing you can do is just be there for them. It's people like that who need a good group of friends standing by them. <3
You're a really nice person to care this much about your friends. There's not a lot of people out there who are like that anymore. -_-
So yeah, just be there for them, litsen to them and help them the best you can.

I hope that helped. ^^