PleaseHelp.My friends an alcoholic?

I have someone i've been friends with for many years.She'll go a few months without drinking then she falls off the wagon.She gets very mean and nasty and will do everything in her power to make your life hell.She'll call when she's sober and tell you she remembers nothing she was in a blackout.Part of this I believe but it seems to me she has selective memory.I tell her all shes done to me and not to call me when shes drinking.It has been two weeks since i've talked to her and she still leaves messages on my answering machine.I keep on forgiving her and take the abuse but i'm tired of it.What should ido when this woman keeps making me feel sorry for her??