Think back to what it was about her that drew you to be her friend to begin with. Did you enjoy being around her then? Did you have a good time and feel that she was there for you when you need a shoulder to cry on?

What is it about yourself that you don't like.. i mean if you become jealous and immature when you are with her.. as well as materialistic, why is that? Why would you be jealous unless you feel inadequate somehow?

I just want to bring a few things up so you can think about what it is causing you to become a person you don't like. Is it her fault? or is that you feel insecure?

She can't possibly understand you giving her the cold shoulder if you haven't been open with her about whats going on with you. True friends can tell each other everything.. not just good stuff.

If you think it is best to just end the friendship, find a way to tell her that. It isn't much different from telling a guy you aren't interested when he is in love with you. You wouldn't continue to lead him on to think he has a chance.

I hope you find a way to work it out without anyone's feelings being hurt. Good Luck!