What does it mean when a guy observes every little thing I do?

Anonymous
So I can't help but notice that this guy I know seems to be super conscious of me. He notices how I talk, move and when I talk to some other guys, and I know he notices this because he either copies me or becomes weird about the other guys. I also think he observes my facial expressions closely enough, I catch him looking at me while I'm thinking often.
I noticed that he buys similar stuff to mine - not kidding. Either he had it at home already or he bought it new, I don't know, but whenever he sees me with new stuff, a week or two later I see he has a very similar thing to that and replaced the old thing with it.

Lately he's also been staring at me very seriously while I was talking, but he didn't seem angry. Just very serious.

And when we're in a social setting and I move a bit, he moves immediately too. I feel like he's observing me quite a bit. He knows far too well when to stand up so that we meet each other when walking out.

Are these serious feelings?
What does it mean when a guy observes every little thing I do?
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