How to know if a guy likes you or just wants to be a good friend?

I have this guy friend, who has lately been quite close. He calls randomly to ask answers to questions, or let me know about a new episode or sometimes just to talk. He teases me, at times be close but not always. He mentions about other girls to me but not as much as what I hear him say to others. He talks seriously with me and asks for my advice. I have only been out with him with a bunch of friends. He is younger than me by a few years but I see him matured in some other ways. I didn't have feelings for him in the beginning other then just being a freind but lately I have been smitten by him. So how will I know if he is just treating me as a good friend or trying to take it to the next level?