What in the _ is wrong with me?

So i work with this guy and he is pretty nice. He has had is heart broken before and isn't actively look ing for love. Same goes for me. Now that i've briefed you here goes my dellimma(sp). I knew him in highschool i knew he had a slight crush on me. Been working together now for a good 5 months and have hung out once though he often asks when im free. Up until a month agao i would have said that i wasn't feeling him too much and up until a week ago, because we have been flirting heavily for a month now (not just one sided anymore), i would have said he was just possibly someone i could have some casual no pressure fun with. Someone i wouldn't think about too much. But a week a ago he went away and i suddenly found myself missing him intensly. im constantly thinking about him even outside of work and antisipating his return. Im wondering what in the H E double Hockey Sticks is going on here. Do i really like this guy this much or am i just infatuated? Is it too soon to tell?