What to do when the friend's gotta go?

So I have this friend. (Funny way to start out) And I feel we've really growing apart. I feel I've matured and she hasn't. She's always complaining to me about boys, her life, her other friends and situations and we rarily ever talk about me or what's going on with me, I get the feeling she basically doesn't care. I just think we shouldn't be friends anymore, because really, I don't feel its even much of a friendship. Its basically she calls me up, complains and whines about herself and I coo and baby her until she feels better. She just negative about everything, and that also makes it hard to tell her good things because she always brings it back to her and how it means her life sucks. That's how almost every conversation goes. The only issue is how to tell her how I feel without having a big blow up. She doesn't have a lot of friends and I feel bad to leave her hanging. I have an idea of what I have to do, but I thought it would be good to get some input.