goodgrl (sensing not so good now.....;))
Anyway,
i'm 21 and understand what u said and are trying to say.
I think there are loads of girls in ur situation, been in it myself. As previous posts have stated it seems that he doesnt want anything serious and i wouldnt fall for the odd BOOTY CALLS (for the oldies - when someone rings u up simply to get you round for a bit of "slap and tickle", without the Ploughmans lunch.....).
If you're looking for something more serious, like a relationship then i'd move on to better things.
It seems like he's just doing enough to keep him on your mind so you dont get over him, whilst he's out there probably checking out and meeting other girls.
Men tend to have this sensor which goes off everytime you're about to move on which means it's time to send you a message...
Dont fall for it - dont reply to his messages and move on.