Guy stares and doesn't look away? He glanced at my lips?

I know this guy and I caught him staring. Then I looked away and then back at him and he was staring. He had a little bit of a closed mouth smile on his face and he was looking all innocent. I look away again to see if anyone else around me notices that he is staring. No one else notices. I look back at him... he is staring. At this point I'm confused... but stare a little longer. He looks from one eye to my other eye, glances at my lips, and then stares back into my eyes. He had the same smile on his face the whole time. I look to my right to see if anyone is standing over there... nope. I knew there was no one behind me because there was a wall behind me. I look back at him and he is still staring. He did not look away. I don't have a lot of experience. What was he thinking? Why did he glance at my lips? I wasn't talking or anything. Was he thinking I look weird? Was he flirting?
Guy stares and doesn't look away? He glanced at my lips?
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