There are a lot of things at play here, so try not to get too worried over any one small event. He could have just been having an off night or if he is like me, the first day back is always horrible... I don't know, I can't see his body language or hear the inflections in his voice or what he is saying... Sometimes with a fast moving relationship the slowing down happens, maybe you realize that you don't know all of the little things that you would if you moved slower or it is the drag of have a long distance relationship. They are hard and not for everyone. The best thing is to just talk to him. If this keeps up tell him that you feel there might be a distance growing between you or that you feel the spark is slowly going out... There are so many could be's that you could be driving yourself up the wall, so it might be much better to just get it out in the open and find out the truth....