This absolutely breaks my heart every time I see it. Because I’m pretty sure that this is the exact moment when Sherlock realizes he’s probably not going back to Baker Street for a very long time, and that he’s going to be separated from John.
This entire life that he’s built for himself with John comes crashing down
And the worst part: He can’t tell John anything. John is his confidante, his best friend, the only person who appreciates his crazy deductions, and the only person who puts up with him playing the violin at 3AM or putting body parts in the fridge … and he can’t tell him anything.