I have to ask a couple questions first?
Is he a lot older than you. Or maybe he is an only child.
Does he only hook up with you at work?
Do you feel he is kind of keeping his distance from you in certain areas of his life?
It sounds like he is having trouble treating you as an equal
partner in this thing. Could be he doesn't have the experiance.
Could be he is very caught up in his own stuff and just isnt really that
interested into getting into something steady.
Perhaps, you could talk to someone who really knows him.
His brother, his favorite teacher, his best friend.
Do his friends treat their girlfriends the same way?