You know when John gets so angry he does that scary smile that only he can do? Well, he looks like he's doing that here.<= this is not johns angry face. This is the 'I know something you don't know' face.
this bit makes sense, John thought maybe, MAYBE, Sherlock was on the mend; that he was on his way to being a normal human being. But now he can see the cold hearted thought process and he sees now how Sherlock has regressed. ---> THE FEEEEEELS