A guy smiles at me in passing. I catch him glancing across the gym but he never tries to talk to me how can I know he is really interested?
He might just be shy. Start a conversation, introduce yourself. Ask him one step at a time though. C:
He's probably interested, as a guy I've done that many times before. But try to talk to him often.
Try to get him to talk to you, and try to sit as close as possible to him just so he can notice you an maybe you can talk then?
Smile back or say hi when he passes.
That's not enough to say that he likes you, it might just mean that he's being friendly
He's probably shy, Next time he smiles at you, say hi,
Sometimes you have to be the one that initiates these things. There are hunters and trappers in relationships. Hunters pursue, Trappers lay in wait. He may be the latter.