Your brother needs help and treatment in the form of therapy and medications too, this is pretty clear. But how do you open a channel with him?
I suggets to forget the "feel good bullxit", as he says. Don't say he is wrong, becaseu he is not wrong. When somebody says his life is crap, it's better say "yes, you're right. but since we'll be still here tomorrow morning, we should get organized, so you can suffer less. we/you really should, because what is bad can always get worse". It's not a matter of faking agreement to win trust, it is acknowledgment of a fact. If life is not crap in itself, HIS life surely is.
You may try to relate this way.

Good luck