What does it mean when a guy that likes you and wants you so bad but you dont like him and he is all pissy now?

This guy iv known my whole life just confessed that he loves me all my life and meanwhile has a girlfriend but he's a player and i told him he's unfaitful becuase of what he's doing to his girlfriend behind her back and telling me he wants me so bad and a whole bunch of stuff and BULLSHIT and i know for a fact he'll be bord in a couple months and do it to me so what should i do he wont talk to me now and he's being a real jerk!