Why would a guy keep staring at a girl who rejected or ignored him?

There’s a guy I sort of rejected one day at the gym but he still kept smiling and staring at me after that when he saw me. He would look at me with this like entranced stare and follow me with his eyes. Why am I still on his radar if I wasn’t reciprocating? He seems like a great guy but I also want to be cautious since we go to the same gym.
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+1 y
He’s still looking at me and I rejected him like 5 months ago
Why would a guy keep staring at a girl who rejected or ignored him?
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