I have to agree that it sounds like he's using again.
If he is, it's time for you to make a choice for yourself. You can either allow yourself to be dragged down with him and bring the turmoil and drama back into your life or you can decide that you're not going to be a part of it.
He is an adult - he is capable of helping himself if that's what he wants.
You need to take care of you!
I sometimes worry that my dad is going to start using again. He's a grown man who has been given every opportunity to help himself (sounds like the same goes for your brother). If he did start using again I would have to make some hard choices - I would have to choose me. It would be hard but I know it would be the right thing to do (for us both).
It's a crappy situation to be in - I truly feel for you.