Your brother sounds very much like my brother, although mine doesn't work much these days, he has his own business and used to do very well.
He calls me when he feells like it and just launches into talking about how hard things are for him, how everyone is against him, how the whole world is designed to get him down even. I used to respond and try to talk to him, explain how things aren't really how he sees them, but fortunately I learned not to, if I have time I just let him ramble on, other times I tell him I'm busy and can't talk. One time I told him if he decided he really wanted to stop drinking and rejoin real life I'd back him all the way and be there for him as far as I could, and now I always end the conversation with ' you know where I am if you really need me' not for his sake really but for mine. I don't feel guilty any more about not talking sometimes, I know I've told him I'm here and I care. And I don't dread the phone ringing like I used to.
That probably doesn't help you much, but I just wanted to say you're not on your own. I know how you feel. It was difficult at first for me to more or less say 'look sorry but I have something more important that needs my attention' but it's the truth, I have me and my family and I have to look after us first.
Don't beat yourself up over his call, he knows you're there and that you do care.