Hey. Lorraine is right when she says that hurting yourself won't help your brother.
My Dad brought me up on his own between the ages of four and ten, then I went to live with my Mum and she brought me up with my step-dad from then until I became an adult. They weren't perfect, no upbringing is, but would you say that they're to blame for my difficulties? I certainly don't blame them, and I don't imagine you would treat them with the same contempt that you're treating yourself. You don't deserve to beat yourself up because your brother has his struggles. They are not your fault, just as my struggles are not the fault of my parents.
Same with you feeling unable to help him. You can be there to listen, but really, your brother has to help himself. Same as we all do, when it comes down to it. We are adults and, most of the time unless we are completely not in control of ourselves, we have to take responsibility for our own mental health and well being. It's the same for your brother. It is not on you to "fix" him. It really isn't.