Hi allme, I've got to agree with the others, you really need to put yourself first. You really have to draw the line somewhere and the longer you allow him to have this effect/drag you in the harder it's going to be for you to draw that line and to take care of yourself. The more he's going to be taking from you.
And as for the guilt..........well you have already tried to be there for him, but there has to be a point where he starts to take some responsibility for himself. Now obviously that might not be easy for him, and without your support/being there for him he might even get worse but maybe that could eventually lead him to standing more on his own/getting help. You've heard of the "tough love" approach, right?
And he doesn't really seem to be using your help right now in putting things more together for himself anyway. But taking a step back from him doesn't need to mean you're "abandoning" him. Not responding to messages (trying to ignore them) doesn't mean you're going to do that with every single message that comes through, saying you haven't got time for/can't do........and he needs to talk to/find someone else doesn't mean that you're never going to give him some time/do something for him, telling him he can't stay with you again if he asks doesn't mean you can't still catch up with him.
And let's face it, you're not asking for too much from him are you e.g. giving you some space, respecting your feelings, caring just a little when you have problems, trying to help himself.........??!! Afterall he is your brother!!!
And, from a distance, you can still be throwing information at him about other support he can get e.g. with his addiction. And if there's a time you have real concerns about his mental health/addiction and think he's putting himself at real risk, he's not going to thank you for it, but in his best interests you probably should be letting someone e.g. Social Services know anyway, right? There is only so much you can do.
So, time to think about you a bit more, yes?
Time to try to kick the new drug? Time you had some support, hey?
And here for you..............
Alison