I understand your confusion right now. Since you don't quite understand the difference between helping and enabling, I would suggest a couple of wonderful books to help you identify the classic role of codependence.
Codependence No More by Melody Beattie
Getting them Sober by Toby Rice Drew
Unfortunately your brother is doing what alcoholics do.....he is using you and he will continue to do so as long as he is permitted. You understand your boundaries in regard to him but he is stomping all over YOUR boundaries. You sound like a wonderful human being. A kind, caring, loving person who sacrifices for themselves in order to give or do for others.
It is difficult to understand until you do some reading or go to some Alanon meetings, but when you concentrate on doing what is right for YOU.....it is the kindest thing you can do for your brother.
I am the mother of an adult alcoholic son. I have enabled and protected him for years. Unknowingly I supported his addiction with my love and constant assistance. It was very difficult for me to change those behaviors and I have to work at it daily. He is currently in an intensive outpatient program.
A year and a half ago I never would have believed that there was a wrong way to love or such thing as loving too much........but there is.
You do have choices........and you are not alone.
gentle hugs