Guy's Behavior

Why does he copy everything I do and say?

A guy I have been friends with has been acting strange lately. He rememebers everything I say and quotes it whenever he has a chance. He uses my lines and my jokes. Not only that, but whenever I say I like something, he likes the same thing. For example, I said that I like when guys wear dressy shoes with jeans, next time I see him he's wearing dressy shooes with jeans. And this is someone who wears sneakers all the time.
What is his problem? I'm starting to feel weird about this.
Why does he copy everything I do and say?
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