Why does he do that?

I have a guy friend. When we meet up together and chat, we have so much fun and I can feel that he values me as a friend. But in places like university or some situations like people who we both know present, he isn't sincere as he was in our meetings. He says hi or something but doesn't smile like he used to do. And it makes me think that he doesn't like me anymore. But then he texts and says that he wants to meet up again. And it goes like that. What should I do? Should I ask him if I make him uncomfortable?

Why does he do that?
Post Opinion