I'm sorry that this is a short reply. I just wanted to say that I'm thinking of you, because I'm in a similar situation with my Mum (though she is getting suport) and it is hard. I guess what I am trying to focus on is that me staying well is the best thing I can do for my Mum right now, so I have to detatch myself a bit. I can still care, but I can't get obsessed with how she's feeling etc. It's the same for you. The best thing that you can do for your brother is to stay as well as possible.
Sending a hug.