Why is it that my friend keeps liking and disliking me?

My best friend (She is a girl) has been friends with me for many years. Just recently she began doing something strange... For a week she would continually flirt with me and talk about us dating. In fact she would follow me around and only say how much she loved me, I thought that she you know had a obvious crush on me so I thought I should tell the next week that I wasn't interested but that very next week she completely ignored me and started flirting with another one of her friend. I thought she got over me but the week after that she started doing the same thing and continually flirted with me. This has been going on for many weeks were she falls head over heels with me and then another friend, she also dated most of the kids in our class since she said she had crushes on all of them.

Why is it that my friend keeps liking and disliking me?
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