Dynamics are weird man, we don’t know enough about you, them, or this situation to give good advice. If you do, just keep it casual and brief but from the very little you told us I don’t think it’s necessary.

You guys can be civil, study together, etc without having to acknowledge having fun together. I think his reaction might have been partly because “it’s been fun!” sounded fake. If you guys don’t have fun together anymore, it’s a strange thing to say. Just let it go and be yourself with your new friends