Maybe after the Reinchenbach Falls Watson convinces himself that Holmes is alive and that it is all a farce and that Holmes is too great for death because isn't he? He cannot die, he wouldn't let it happen, would he? And after so much time consumed, so many sleepless nights and so much stress and tears and just paranoia that Holmes would be there, alive, maybe Watson finally gives up.
Holmes is not alive. No one survives a fall from that height. And at least Moriarty is dead; Holmes died with a purpose, he'd conclude, eventually. And that hurt as much as (more than, really) the distant possibility that Holmes was alive. He isn't. So maybe Watson gives up and continues his life, but a part of him is missing. And that part of himself replays how Holmes must have fallen (Watson wasn't there. Why wasn't he there?), debated if Holmes died drowning or if the impact of the fall was enough to do it. And the image of Holmes' cold, dead face was all he could think of sometimes, and the sound of the water as it conducted his limp body through the river often woke him up sweaty and trembling. But life continues, it has to.
And maybe when Holmes does come back, breathing and very much alive in the same room as Watson, maybe he's even more destroyed because he had been right and he stopped looking and he shouldn't have stopped looking and. Holmes faked his death? He did, and hid that from Watson and maybe that's a bit much for him to bear but he'll make it. Because Holmes is alive and breathing and talking to him and that's all that matters. They're together. Maybe sometimes he looks over to Holmes and sees death in his face and his body threatens to betray him but he resists. Holmes is alive. And breathing. They're together, now.
