Awarkard silence! Incompatible?

So I like this guy. He speak to me most of the time. Some times I can see him watching me from across the class room. It seems as if he kinda follow me from one side to another. (Not sure). He speak to me and smile but we have a few seconds of awkward silence and the last time he walked of after I said hi and how was his family. He spoke and smiled then things got quite and we just looked at each other and he just walked off. I'm so confused. We have had small talk before.