This should be inconceivable.
Futile to even think of.
Yet, living with Sherlock has shown John that the impossible is actually more likely than he originally thought, and this moment is the cementing of that revelation: Sherlock Holmes, thought by the entirety of London-including John-to be dead, is standing on the doorstep of 221 Baker Street, looking for all the world as if he had just returned home from solving one of Lestrade's cases for him.
John cannot speak past the lump in his throat, can't figure out which of the emotions coursing through him to give in to; the shock that Sherlock is standing there, alive and moderately well in front of him, anger that Sherlock had apparently faked his own death and waited three bloody years to finally show his face, or the overwhelming joy that Sherlock was alive...
It's too much and not enough; John wants to demand answers, shake the truth out of Sherlock as he calls him every name he ever learned in the army and a few he made up, he wanted to embrace the git, squeeze him tight and admonish him for making him worry and demand that he never do anything like that ever again, and he also wants to punch the bloody bastard in the face for making John watch-
In the end, the decision was taken out of his hands as Sherlock decides to collapse right in front of him, making John's heart lurch so painfully in his chest he actually feels it like a physical pain and he's moving without any conscious thought on his part.
This time, when Sherlock falls, John catches him.
The feel of Sherlock's body-solid, warm, real-against his is too much for John and he feels his eyes well up as Sherlock's fingers grip John like he's a lifeline, as Sherlock's gaze focuses on him and for a blinding, heart-stopping second, Sherlock's lips quiver into an honest-to-God smile!
The tears finally fall as Sherlock uses his last bit of strength to utter a single, soft word that brushes warm air against John's face like a cleansing breeze:
A/N: Next time I get writer's block, just lock me in a room until it goes away...