Why does he stare at me but never approach me?

I've noticed this guy staring at me quite often on the bus (we live like two bus stops away from eachother). He just gets on the bus and stands near me even though the bus is almost empty, and he looks at me while being on his phone. He never smiles though. I think he's even talked to his friends about me, because sometimes I've caught them giving me quick looks. How do I get him to talk to me? I'm quite shy so I can't start the conversation myself, besides, it would be embarassing because of his friends.
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I know his name but he doesn't know mine. Should I follow him on instagram?
Why does he stare at me but never approach me?
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