How do you know if there's a mutual attraction or if it's just one sided?

There's a guy I really fancy we exchange stares. He has found excuses to speak to me/ presented himself with open body language. He stares upclose sometimes but mostly observes from far. I feel something but I don't know if it's just one sided and if I'm just really attracted to him.
How do you know if there's a mutual attraction or if it's just one sided?
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