What is the difference between leading a guy on and just being friendly?

This guy and I have been chatting on FB. we go to school together. He mess's with me alot like he takes my pen ang pan grip.He's usually brooding and cynical but he's being really nice to me when we chat. He's seems really interested in my love life. (BTW I don't have a boyfriend) I don't want a boyfriend either. He's keeps saying when you like someone please tell me. I seriously just wondering am I leading him on or am I being friendly/ I am also wondering does he like me?