how can I be nice about the fact that I want to stop talking to tara?, and stop being friends with her

it was a good idea when we started talking- she seemed nice and she seemed like a caring person

but now I find out that

A she only uses me when she wants help with something, and even when I offer to help her she turns me down and tells me she'll wait for her boyfriend who hardly even talks to her

B she lied about her mental illness which both her and her friends have told me, and tara herself said she used it to get attention

and C, she's rarely interested in what I do- it's all I did this, I did that, etc. I try to use her for support, but she's rarely interested.

the problem for me, the biggist problem, is that she's always calling me best friend forever, awesome friend etc

she even plans what she wants to do with me ahead of time.

I don't exactly want to be horrible to her, but I do want to stop being friends with her and let her know gently that she's just using me for when ever she needs to talk or for when ever she needs help

what would you do