Why isn't he answering mine bantering?

We used to be very close and we teased each other all the time. Our banters were highly sexual sometimes. He was the one starting it, and doing it all the time. All of a sudden he stopped. We are still very close, he confides in me, but our talks are about more serious stuff. We never fool around anymore. I try to provoke his reactions but he never answers them.
Once I accidentally said something that was understood as an innuendo by other guys, but he just looked at me (he thought of it the same as others did) but said nothing. Others commented that it was the first time he's left speechless and they laughed about it.
I also noticed he never looks me in the eyes like he used to. And if he does, he blushes like hell.
What is going on with him? I miss his goofy self.
Why isn't he answering mine bantering?
Post Opinion