You said you wanted to take all his pain away, but you couldnt. And if he was alive, you still couldnt take his pain. But you didnt failed, and he didnt failed, too. The pain is gone now, he is free, finally. I dont know what problems he had, and waht caused his pain, but i know that its not your fault. The task is completed now, the pain is taken away from him. Just try to beleive that he is on better place now. Even if you are not religious (im not), remember that even if he is nowhere now, even if he doesnt exist.... sometimes nowhere and nothing is better than constant pain. If he knew a way to make things better, or if he thought there is help for him, and if he thought that you can help him, trust me, he would off asked for it. I guess he choosed to die to set himself free, but also, besides he knew he will hurt you, he was hoping that you will understand why he did what he did, and in some way, he did that for you, and all people around him, so everyone can continue walking on his own path. Would it be better for you to see him suffering everyday, and to suffer with him every day, or now, knowing that he is gone, but his suffering ended too? I know the answer of this question is hard, and you will never be 100% sure, but i think you know waht your brother would want you to beleive in. You didnt let him down, dont let him down now when he is gone.
I have a sister too (dont know if you are his sister or brother). And i know that when im gone, i want her to forget me as soon as possible, and to be happy for me, to be happy that im not sad anymore...