I liked this guy, we held good communication at first but something changed, what could it be?

Ok so I liked this guy and everything went well at first until suddenly he stopped talking to me (guys always do this, I know. but this is sord of different) in my perspective I think it's because I suddenly became really nervous around him that whenever I would talk to him things just got worse I would say stupid things or sometimes i just couldn't think of what to say, could this have made him withdraw from me even more? Now things are cool....i think but I still hurt because i didn't want him to stop talking to me, he's such a cool guy and who wants to lose a friend? we had a thing starting and he just blew it off, I want to move on but I still want to know why. Why would he do that?