Although he only mentioned it once, Sherlock's retirement plan for John and himself of moving to Sussex to grow old and raise honey bees together is extensive and meticulously detailed (because Sherlock is the sentimental sort, no matter how much he denies it or other people reject the notion.)
Everything falls to shite (both figuratively and literally) when Moriarty threatens John (the first time of course because Sherlock gets too attached too quickly and it always ends in disaster *see: Redbeard) and Sherlock can't stand the thought of John being killed because of him so he plans and schemes and acts like a cold bastard to hide his fear, and, eventually, when there's no way out, he jumps (and it's not at all like flying.)
Over the next two years Sherlock travels everywhere, from Africa to Asia, Australia to the America's, and the only thing he wants is to go home (because home means John and 221B and fresh tea and giggling at crime scenes and John.)
He doesn't get his wish until he's nearing his third year away and a Russian is torturing him (and he can honestly say he's never hated his brother more than at that moment.)
When Sherlock finds out John doesn't live in 221B anymore he turns so Mycroft doesn't see the surprise he tries to cover with iciness and sarcasm (and he definitely doesn't let himself think about the heavy weight of dread that settles itself over his heart at the thought of John moving on from him), and when he finds out where John is going to be he doesn't think, doesn't plan, just goes (because with John he's never been logical, never been able to completely separate himself from his emotions; it's always jump first and deal with the consequences later *see: Reichenbach.)
Sherlock sees John for the first time in two years in a restaurant, sitting at a table waiting for the woman he loves and is about to propose to (and doesn't that just bite?) and he panics (just a bit) and devises a crack-ass scheme that will most likely end with John's fists leaving bruises on Sherlock's face (and that's exactly what happens and it hurts because even though John was an army doctor, he was in the army and "[he] had bad days too!")
He can't hate Mary. She was there for John when he wasn't, she helped him grieve and heal and is infinitely better for him than Sherlock could ever hope to be, and, most importantly, John loves her, and that is enough (it has to be.)
John asks him to be his best man and he can't say no (because after all this time, after everything he has put John through, John still has it in him to forgive Sherlock, so Sherlock will do anything to make sure he doesn't destroy the happiness that John has built with Mary.)
As he leaves the reception early Sherlock can't help but ponder on Mrs. Hudson's friend (if she had been in love with Mrs. Hudson like he was with John and just couldn't bare the sight of the happy couple as her own heart felt like it had been trampled on by a raving stampede of elephants) and, as he pulls his coat tighter around himself, Sherlock wonders if any of it mattered (the games with Moriarty, the falling and subsequent grief it caused, the two year hiatus of his life, and the returning.)
(He doesn't think it was.)