What does he mean by this behavior?

There’s a guy at work works in a different department but I run into him sometimes sometimes we BREIFLY communicate I don't know I thought he was cute so I tried to get his socials n he was like I have girlfriend but ……… he continues to act like really weirdly and I seem him have a lot of friends that are girls he stares at me a lot a lead paint stare and sometimes cranes his head just so he can stare at me sometimes he acts annoyed with me he will just stare sometimes I’ll stare back but mostly I mind my business and especially now since I know he’s taken I’m just wondering what the hell is he looking at? And what is he thinking?

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There he walked outside with me and walked in so he could hold the door for me and a few other people but he would not stop holding eye contact with just me and he continuously we come into circumstances where he will hold the door open for me and then looks at me like he wants me to say thank u but I don’t lol

Another time he was on his phone in a room full of people and he put his phone down just so he could stare at me

Another time he turned his head literally 180 degrees looking at me
What does he mean by this behavior?
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