Are we really just friends?

i think I have a big problem. my best friend have known each other since fourth grade but we live a long way from each other so we keep in touch through Facebook. I know were supposed to be "just friends", but sometimes I get really tempted to kiss him, and I get jealous when he finds other girls hot. we flirt sometimes when we chat, but he always says that he wouldn't get jealous over my other guy friends because "after all we are just friends". what am I supposed to do? I really don't know how he thinks about me