Title: Burn Your Heart Out
ONE
Moriarty had finally lived up to his promise, Sherlock decided, as he felt his chest explode over and over, in waves. And he'd done it in style. This wasn't just fire, this was acid and everything else that burnt. Ten years ago, Sherlock would have been able to give you an eighty minute, thirty two second lecture on every substance in the world with the potential to burn, with charted diagrams, live demonstrations and a joke far too intelligent for everyone except himself and Mycroft.
But right now, as he watched John sobbing over someone who wasn't him, he didn't give two fucks about the details of what was happening to his heart, because he knew.
Four years ago, John met Lucy. Three and a half years ago, they had bought a house together. Three years ago they married, sans Sherlock. Two years ago, Lucy had been declared fertile. Thirteen hours ago Lucy was killed on collision in a hit and run. Three hours ago John had begun sobbing on his sofa.
Four years ago Sherlock's heart started burning. Three and a half, he discovered what rejection felt like. Three, loneliness, two, small victories. Three hours ago, he discovered what longing for death felt like.
Sherlock shakily stood up and clambered towards the bathroom and vomited into the toilet.
Then he walked back out and turned and faced John.
"Doctor Watson, I'm afraid you are going to have to vacate the premises."
John looked up and another wave of acid showered over his heart. His face was tear-streaked and rumpled.
"You really don't know, do you Sherlock. You really don't know what it's like to love someone so much that it makes you physically sick when you aren't with them, what it feels like when they leave you forever-" but he was cut off by a hiss from Sherlock.
"And you are really too stupid and too blind to realise that I feel it every single day."
They stared at each other awkwardly for a long time, before John whispered, "Who?"
"Oh don't act like you don't know," Sherlock bared his teeth and stalked out of the room.
TWO
John moved back in three days later and it should have been the highlight of the decade for Sherlock, but all he felt was disappointment. He hadn't attended Lucy's funeral, but he'd seen John afterwards, and it was just another reminder that John could never love him like he'd loved Lucy.
A month and a half later, John discovered Sherlock's nightly ritual of crying into a shirt, which had begun eight years ago. He hadn't stayed long enough to recognise it as one of his own.
A year later they were as back to normal as the two of them could get, given that Sherlock was a heart-broken sociopath and John was a bereaved ex-army doctor with no children.
One afternoon they were sitting in the lounge, Sherlock blowing smoke rings and John inspecting his almost-grey hairs in the back of a spoon, when Sherlock popped the question.
"What would you do if I died?"
"Cease to exist," John answered truthfully and immediately, as though he'd thought about it in great depth.
John purchased a puppy once. He was, in Sherlock's opinion, awful. Fat and rumpled and name Gladstone. It wasn't until Mrs Hudson quietly mentioned how much he looked like John that Sherlock had begun to warm to him. He was, after that, in Sherlock's opinion, perfect.
Sherlock got a boyfriend shortly after this. John began to copy Sherlock's nightly ritual, which Sherlock politely ignored.
Every year, the anniversary, John would go down to the graveyard. This killed any hope Sherlock had ever regained instantly.
John had one other girlfriend in his life - surprisingly, Sarah. It lasted three months, and then John shagged Lestrade out of growing frustration. That was the end of that.
Sherlock tried to keep bees in the flat at some point. Mrs Hudson nearly killed him, and Gladstone didn't cuddle him for a week.
John was never sure why he cried over Sherlock and Victor. Loneliness, probably, or jealousy. They were a handsome couple, both far younger than their years. Sherlock would certainly not want John anymore, what with his grey hairs and rising body weight. Sherlock had moved on.