That sucks...I'm about to lose a family member soon(grandfather is very very ill...terminally ill)...I wasn't particularly close to him though since I didn't even really meet him until I was like 13(technically I did meet him earlier but I was under 1 years old so don't really remember), and he lived in China...he did live with us for a year though here in the US although I guess I never really talked to him. But still, it's not really a happy thing to have anybody die.
Although I'm sure it's far worse in your case since you probably knew your brother better, and he's a young guy, while my grandpa has lived a pretty long life by now.
Anyway, definitely look after your little bro...maybe some kind of therapy/counseling would be good for everybody...don't wanna see your little brother(or you) follow that sort of road out of some weird guilt complex. Anyway, it's not your fault, we can't really be everywhere all the time and know everything. And CPR/Rescue Breathing isn't a miracle either, it can only prolong life so much... =(
My condolences.