I am letting someone else control my life?

I really love my best friend (platonic, we're both girls), and her opinion of me is extremely important. I tend to act like her servant--it just comes naturally to me. Whatever she wants, I go along with it. I can't tell her no, or maybe I should say that I don't "want" to tell her no. We live together, and I feel like I'm not a free person. I'm not saying it's her fault, because clearly I am building my own prison. It's just that the price of freedom might be my closeness with her. If I live my own life and separate myself from her hip, I'm scared that I might lose her altogether. What should I do?