Can you ever let go, without hurting somebody?

Decisions, decisions, that flood my mind. Not knowing how to tell the one person that needs me the most that I feel it's best that we not be friends anymore. If I do not part this individual from my life, it will only bring more negatives to me. Her drinking, her alcoholism, it's bringing me down. I'm tired of being her babysitter. I used to drink too, I used to be an alcoholic, with her, inseparable, not only from each other but also from the bottle. I'm breaking, just thinking about hurting the person that needs me the most. If I don't walk away, my life is going to fall apart. Drinking, trouble, neglecting responsibilities, I can't do this anymore. Is walking away best? I've tried to help, she doesn't want to stop. I wanted to stop, I did. She doesn't want to, this is the life she wants to live. I do not, how do you chose what to do? I know what's best for me but it's so hard for me to leave those I care for behind. I'm afraid of what she might do, what might happens, if I'm not in her life. I need my family, I need my time with them. The time I've lost, over the four years of being an alcoholic. It's gotten me nowhere. Nowhere to where I wanted to be. The only thing alcohol has gotten me was two duis, house arrest, a suspended license, dropping collage classes, quitting a full time job, ruining relationships with successful men, distrust from my family, depression, a reputation. These are what I have to show from my addiction. Nothing positive. I have changed, I do not get drunk anymore. It is not important to me anymore, I'm trying to get my life on track. I'm trying to do what's best for me. I want to be a success. They say to surround yourself with those who uplift you. I feel like my best friend is standing in the way of my success. I've been her everything for four years and she's been mine. How can I just walk away? Especially from somebody who has an addiction? Just give up on her? I don't think that's right either. I just want to learn how to do what's best for me without hurting somebody else. This is my life, this is what's weighing on my mind, holding me back, hurting.
I will figure this out, it just may take time.