Sometimes there are fractures that cannot be healed and scars that will never fade.

For example, there's the fracture that Sherlock leaves in John's chest as he dies.
It's a fracture that's never going to be healed because it's simply too big and complex. When your soul mate dies, you die with them. It's a stupid thing to say because it has never been stated, but John's will is made of steel and his faith in Sherlock is as strong as the curse of a god, and this makes the situation even worse. The most important person in his life dies; John dies, too. But he's a soldier and, even if Sherlock's dead, he's going to fight his battles.
John misses him. Of course he does. He's endured worse wounds, though, so he goes on.
It'll just leave an invisible scar on his skin, but he can live with that.

One year after Sherlock's fall, he marries Mary Morstan. He marries Mary because she's lovely, understanding and nice, and because he loves her. It's a really different kind of love if compared to the one he felt towards Sherlock: it's romantic love. It's normal, it's average. It's what everyone was expecting from him and what he's always wanted; even if completely mad and broken, he's a straightforward bloke and straightforward blokes want to have a wife and children—at least, this is what John wants when London is not a battlefield anymore, when he has to be just John Watson and no one comprehends him. It's also a thing that, when Sherlock was alive, was absolutely prohibited to him, mostly because Sherlock had always been more important to him than a steady relationship. They'd always known that and, in spite of John's repetitive complaints about it, they never really cared. It was some sort of mute whisper between a date and another, of silent agreement between a woman and another; it was a long-life commitment they had established without even talking about it. It was perfection. Or, at least, the kind of crazy life that they had wished for.
But Sherlock dies and so does their pact. John Watson marries Mary Morstan because he loves her, but she's never going to be Sherlock and he knows that (she knows it, too).

When John is Mary's husband, he's fantastic because there's no one to remind him that he's awful. He works in a clinic, when he comes home she's always there, waiting for him, and everything's good. He's still interested in crimes and reads a lot of newspapers (because those murders reminds him of Sherlock and of gunshots). Those newspapers are his placebo, those words of blood and death and crime written down on paper are the relics of a life he's lived and that's never going to come back: the proof that Sherlock Holmes existed and that he's been a very important part of John's life, making living at 221B Baker Street the best experience he's ever had. They're the medicine he uses to soothe the pain of his wounds and to mitigate the ache of the agonizing flower that is blooming into his bosom, the flower of anguish and nostalgia. Mary understands that or, at least, she pretends to, which is precisely what makes her one of the most lovable creatures John's ever met.
He's never going to grow old with Sherlock, but maybe he can do that with Mary; growing old with her, filling their house with a family.

Truth is, their marriage doesn't last, and it doesn't last because Mary doesn't.
One year after their marriage and two years after the fall she dies, taking with her a lot of hopes and a lot of dreams. John buries her, but it's not worse than burying Sherlock (nothing is). But since the world has decided that he's not worth of anything, he accepts it. He's simply too tired to rebel.
There are condolences: a text from Mycroft, a call from Lestrade and another from Harriet, an email from Stamford and an atrociously sad dinner with his parents. He finds Mary's will in a drawer. He keeps living in the same house and sleeping in the same bed.
His love for her dies, too, and in a terrifyingly fast way. At first, John feels guilty, brutal and terrible. But Mary's death is a wound that heals and, with a sense of freedom slowly growing into his chest, he realizes that she had never been that important in the first place.

Sometimes there are fractures that cannot be healed and scars that will never fade.

For example, there's the fracture that Sherlock leaves in his own chest as he fakes his suicide and practically 'kills' John. It's a fracture that's never going to be healed because it's simply too vast and tortuous. When you make your soul mate die, you die with them. It's an idiotic thing to say because it has never been stated, but Sherlock's will is made of rock and his faith in his own decisions and in his power of fixing things are as powerful as the prayer of a demon, and this makes the situation even worse. He causes the emotional death of the most important person in his life; Sherlock dies, too. But he's a genius and, even if he cannot help John now, he has to follow his plans.
Sherlock misses him. Of course he does. He's endured worse wounds, though, so he goes on.
It'll just leave an invisible scar on his skin, but he can live with that.

One year after his fall, he travels to various places in order to track down Moriarty's web. He travels to Florence, where he visits monuments he doesn't appreciate, full of mosaics that make him feel nauseous and make him want to laugh at himself because of his love for the syringes, and kills three men. He lives in terrible places and hides wherever he can, working during the day and shooting during the night, always afraid, knowing to be in Moran's sights. He contacts Molly only to be sure that she hasn't told John the truth; she's now useless to him, but at least he hopes she won't be too harmful. He often talks to Mycroft, though: he wants his brother to keep his flat just as it was when he lived there with John. There are too many memories at 221B, and he cannot possibly let them go; there are pieces of it scattered around his mind palace. Mycroft informs him of John's marriage and Sherlock at first feels horribly betrayed, but then gets over it. He gets over the fact that John is normal, after all, and that he still believes he's dead (he believes in him, too). He gets over the fact that John needs someone in this period of his life: he's broken and damaged and it's all his fault. Sherlock comprehends that John loves Mary Morstan romantically and that what they had was so unique and so spectacular to be above everything else. She's thankful to the woman, actually, because she seems to be able to keep John together. And since he's selfish and horrible, he also knows that John will leave her when he comes back. If he was a good man he would just let the doctor go. But he isn't a good man; he never has been.

When Sherlock is a killer, he's awful because there's no one to remind him that he's fantastic. He hunts the men and shoots them, when he comes 'home' to rest the noise in his head doesn't let him sleep and, even if he deduces an awful lot of things to find those criminals, it is not enough for his hungry brain. So he reads tons of newspapers, silently deducing the killers, the weapons and the motives, going beyond the words of blood and death and crime. Those newspapers are his placebo, the proof that he once was the great detective Sherlock Holmes and that he's lived a period of absolute delight at 221B Baker Street with a man named John Watson, a man that being normal but not average defies all the laws of human behaviour and society. A man that he's broken and is trying to go on with another normal human being whose name is Mary, hoping to grow old with her because he cannot have Sherlock. A man that someday, being cruel and egoist and tremendous, he's going to take away from her, break again and fix.

Truth is, he doesn't need to do anything about Mary. Two years after his fall, she dies. He personally asks Mycroft to say something to John because he can't. He wouldn't know what to say in any case. "John, I'm sorry for the death of a wife you were never going to love in the way you love me"? Definitely a bit not good.
Two years after his fall, he travels to Tibet and meets the head lama; he travels under the fake name of Sigerson; he travels to Persia and to Montpellier, where he actually has the time to experiment on coal tar derivatives. He's killed every single man he had to kill, except for one: Sebastian Moran, who's his personal tiger and obsession. Moran brings him back to London, and he's tempted to visit John, but resists the urge.

Then, three years after the fall, three years after the final act of their personal tragedy turned into a comedy and into a tragedy again, there is Ronald Adair.
Both Sherlock and John pick up two copies of the same newspaper and they're unconsciously meeting again in the ink and in the article about that man, about a city boy who had not an enemy in the world but got killed nevertheless. There is something very odd about this case and while John doesn't know about it, Sherlock does, and he does because he knows that Moran is a sniper and a quite wise one. This time, though, he's asked his brother to help him, and Moran is practically under their gun sight, about to get caught.
Sherlock visits the crime scene in disguise and for a second he's certain that John has recognized him, but the doctor doesn't say anything and neither does the detective.
Then, since the time has come, he asks Mycroft to bring John to their old flat in an impetus of drama. He's going to wait for the doctor there, playing his violin in some sort of encore.

It's night. London is quieter than usual and so is Baker Street, silently waiting for his return. Of course this is only what Sherlock wants to think, but it feels gratifying.
Everything at 221B is the same, from the skull on the mantelpiece next to the stabbed Cluedo board, from the scientific equipment in the kitchen to the periodic table in his bedroom. Mycroft has kept his promise. Sherlock is not going to see Mrs. Hudson now, though, because now John and Moran are his priorities. She's probably sleeping, anyway. Or maybe she's at her niece's house? A quick look at his surroundings suggests him that she's not there. Good.

When John opens the door to their flat, with the most suffering expression he's ever had, Sherlock is sitting on his armchair with the violin placidly resting on his lap. He wonders what Mycroft might have told him; he hopes it wasn't too harsh.
John looks older, of course, and Sherlock is conscious to look older, too.
There are some really awkward and striking moments in which they don't talk.
Then, Sherlock stands up and just says the doctor's name once, and John's expression changes, according to the fact that he's actually realizing what's happening. His face becomes a mask of hurt and fury.

Sherlock doesn't object to the fist that hits his jaw and to the one that hits his nose and to the one that hits his teeth. He doesn't object at all because he knows that he deserves to be beaten—not because he's lied to John, but because he's lied to John only to fulfill his selfish ego (things could have gone differently, but he decided to play Moriarty's game and win). He doesn't object to the fact that he falls and hits the floor with the back of his head and blood drips from his nose. He doesn't object to the fact that John is over him, clenching his fist on his coat. He doesn't object at all: he wants to laugh.
There are three years of suffering, lies and pain in his fresh wounds and in the blood that is now dirtying his face, his hair and the floor of their old living room; there are three years of nostalgia, desperation and rage in the scratches that are now on John's knuckles; there are three years of nothing and one second of bliss in the bruises they're going to have on their bodies. He wants to laugh and he's pretty sure that John wants to laugh, too, even if they both look as they're about to cry—from both physical and psychological pain.

Sometimes there are fractures that cannot be healed and scars that will never fade.
Sometimes you can be very happy about those marks.

"You better have a good explanation for this," John says in a husky voice. "You better have a fucking good explanation for this, or I swear that I'm going to beat you to death, cut you into little pieces and then bury them in your bloody coffin."
"I have one," Sherlock replies, nearly choking on his own blood. "I have."
"Good. Then explain to me why you're alive, because I'm pretty sure to have watched your goddamn suicide, and why you have lied to me for three fucking years, you utter bastard." John is still clinging onto his coat, but his hands are now shaking.
Sherlock's breathing with difficulty now, though. John lets him go and he sits down on the floor, coughing. "There's a first aid kit in the kitchen," he says.
"What makes you think that I want to help you?" John asks, angrily.
"Because I'm begging you to do so," Sherlock answers. "Please."
John licks his lips, stands up and fetches the first aid kit, then comes back and starts cleaning Sherlock's face from the blood. His hands are still trembling but, even if for one small second the consulting detective is sure that the doctor's going to strangle him, John's touches are gentle. They're gentle when he disinfects Sherlock's wounds and when he dresses them with sterile bandages. They're the touches of a good doctor, after all.
"I'm not going to kill you. Even if I really should," he whispers. He touches Sherlock's nose. "It's not broken. I wanted to break it, though."
"I kind of wanted you to break it," Sherlock murmurs.
They look at each other.

Once again, they're marvels and monsters and they are together. Everything falls right into its place even if everything's wrong and everything hurts. But it's okay now; it's okay because, once again, they're completing each other and creating a euphony of silence and noise from a cacophony of gears and gunshots and of palaces and deserts.

"I want to tell you everything," Sherlock says. "I want to tell you everything and if you won't be satisfied with my answers, later, I'm officially giving you the permission to put my brain in a jar. But I cannot. We cannot talk. Not now."
"Why?" John frowns.
"You read the article about Ronald Adair," Sherlock insists. "You read it."
"Yes, I did. It was odd, it—" John pauses. "You were at the crime scene. I saw you, you—"
"Yes, I was there, but that's not the point," Sherlock interrupts him. "He was killed by Sebastian Moran. He's a sniper and uses a very peculiar kind of gun."
"What are you exactly asking me?" John asks, and it sounds like "Should I punch you again?"
"I'm asking you to run with me in the streets of London to chase him. Everything will be alright, Mycroft's helping me, he's already called Lestrade, we'll catch him, then I'll—"
"You're asking me to catch a sniper with you after lying to me for three years?"
"Yes."
"Why can't the police do it just for once?"
"Because I still have some pride, John. I wasted three years of my life after him."
"I've always wanted to keep your brain in a jar on my nightstand."
"I know."
John sighs. "You're a completely, utterly, totally mad wanker," he says.
Sherlock looks down.
"It's an extraordinarily good thing that I'm just like you." John stands up.
Sherlock opens his eyes wide. "Tomorrow," he whispers. "I'll tell you everything tomorrow. I promise." He stands up too, uncertain.
"Lead me," the doctor says simply and Sherlock would really like to hug him, but he doesn't because he remembers that he's, well, himself.
The detective leads him. He does; he's always done that, after all.
You're amazing, they both think. You're amazing, and terrifying. Don't ever change. I missed you.

The next three hours are made of running, shouting, bullets and handcuffs.
Moran is a tiger and he acts like a tiger, but Sherlock and John are way stronger than all the tigers of the world, and that's because they're a whole. Tonight they have help, too, and there's no way to stop them. This is the night of their resurrection as Sherlock and John after being just Sherlock and just John. This is the perfect night that smells of honey and gunpowder and looks like a canvas painted with blood and sand. This is their night.

After giving up the sniper to the police force and speaking to Lestrade (who looks shocked, relieved and desperate at the same time), they go home.

And, finally, 'home' means '221B' again.

Sherlock Holmes and John Watson are lucky enough to be the protagonists of two fateful meetings. They're lucky enough to make two really important promises that night, without even mentioning them.
Things are not going to be as they were before—they both know that. But that doesn't necessarily mean that they're going to be worse; they're probably going to be better because now they're together again and, even if they're going to hurt each other since that's what they've always done, they're not going to give a damn about it. They know they're going to poison each other, but they also know the necessary antidotes.
They're connected by the catgut of their wounds.

Sometimes there are fractures that cannot be healed and scars that will never fade.
Sometimes you can be very happy about those marks and, even if you try to mitigate the pain, they still hurt like hell.
But you secretly enjoy the hurt and depend on it.