How could you tell if he....?

ive noticed he stares alot and gets serious when he sees me talkin to other guys he actually followed me one time or so my friend said lol but ya i noticed his friends when theyll walk by me theyll point and whisper not laughing tho esp. when hes around i caught my old neighbor wich is his bff hit him on the shoulder and point at me . plz give me like clues and signs when they like you