How to know if a guy likes you?

I’ve been working with him (let’s just say X) in the same company for a long time. We’re in different department but we sometimes run into each other at the dining hall and mostly at the terrace. I catch his eyes on me. He stares at me (I stare back at him) and then he looks away. It happens all the time. I never see him alone just like me but when I do I’d like to smile at him but I am too shy and don’t wanna do it in front of my friends. I don’t know maybe he is checking for signs to take a step. Maybe I am giving him a wrong sign.

I really don’t know what to do. Please share your honest opinion with me.