Long time friends

So i have been friends with this girl just over 5 years. Thanks to her I managed to move classes back in 2009 and managed to make some good friends. At first i would do anything she said and always wanted to please her because she was my only friend and I needed a friend. But looking back on it she would walk all over me and say some things to and about me (to other friends) that i am not too happy being called. Now i think it is almost habit and she still walks all over me and makes me feel rubbish. She makes me feel like my problems are pathetic and like i don't deserve anybody. She still bitches about me to our friends and is just generally a bitchy person. Yet despite all of this we have has some great memories over the years and she can be fun to hang around sometimes. I am also really close to her mum and family and her mum has helped me through some tougher times in the past. I can't confront her because she just cries and then i forgive her again and she does it again. Recently she got better friends with another friend of mine and i felt replaced and i although she makes me feel so crap, i have never been so close to a friend. Today she was bitching about me and my friend because she didn't want us to hang around a girl she didn't like. It all sounds so petty but its making be feel like rubbish and i don't know what to do. :/