Could he be over me?!?

my guy and i have been seeing each other for a little over a month now. We hang out almost every day and in the beginning he was always so lovely. But now he seems to be distant and barely talks to me. When i ask him he says were fine but doesn't still doesn't say much. I don't know what to believe, i know it's not another girl but what does this mean? could he be over me? or is it just faze that guys go through. Im 18 and i have had plenty of serious relationships, i can tell that this is not just a hookup but i can't seem to read him. Help!