This is John's face when Sherlock goes through everything he has deduced about Mary. This is so cruel...
John is wondering how long Sherlock has known all of this and why he hasn't said a thing to him sooner. This is TRF all over: Sherlock didn't trust him enough to share the information with him.
He feels guilty because he's the one who brought Mary into Sherlock's life and she shot him. He also feels like a fool because he's the only one who hasn't seen his wife for what she is. Like in TSOT, when Sherlock deduces Mary's pregnancy, here, Sherlock deduces all the things John should have seen about his wife, a woman he is supposed to know intimately.
John is betrayed by the two people he loves: his wife who lied to him since the day he met her and shot a person who is essential to him, and Sherlock, who couldn't trust him and knowingly let him getting married to a liar. Both of them have just played with his deep issues, making him feel like he is the one responsible for his sad fate.
John is in such a dark place at that precise moment... All those dark emotions inside of him, emotions he represses because Sherlock asked him to. And the two people he loves the most keep beating him and break his heart more and more every second.