Meeting John Watson was the best thing that could have possibly happened to Sherlock. John was the first person to surprise the detective and the first to stay by his side. The first, besides Mycroft, to protect him.
And as much as Sherlock hated emotions, John evoked them. The man stirred something in Sherlock and everyone knew it. Mycroft, Mrs. Hudson, Lestrade. It was obvious to those who liked to think they knew Sherlock. Sherlock allowed the doctor into his home, into his heart, the heart he fought so hard to keep empty and cold. John, his blogger, one of the only people Sherlock considered necessary. And the first to be dubbed friend.
Slowly, Sherlock and John grew to accept their strange relationship. Flatmates, partners in crime-solving, friends. Others would always question it -to John's annoyance-, but at least they knew themselves and each other.
Then, Moriarty discovered the few people who had made it into Sherlock's heart -and the man who held the genius' heart. John would always bring Sherlock running. The detective would never allow his friend to be hurt, even if it meant a personal sacrifice.
Which is, perhaps, what made this so hard. John had wormed his way into an otherwise cold and unseen heart. John had exposed the existence of Sherlock Holmes' very soul and now it could be exploited. Of course, Sherlock had known this was a danger. Mycroft had made it very clear that sentiment was a dangerous thing and was to be avoided at all cost.
Sherlock felt the words of Moriarty like a physical blow. John, Mrs. Hudson, Lestrade -the three most important people in his life- would be killed if he were to live. And, just as Mycroft had warned him, Sherlock knew there was no real choice. Sherlock would have to die.
But Moriarty had missed some of those Sherlock kept close. He had not seen Molly, the ever helpful pathologist, nor had he seen Mycroft, the interfering brother. Who would expect Sherlock to care for them? But they were -however loathe he was to admit it- his friends, and they would protect him, just as John had said friends should.
So he met Moriarty on that roof. Sherlock watched his last chance disappear in the crack of gunshot. The genius had called his best friend, for who could deny that he now had to differentiate between his friends, and left his note. Then he jumped.
Sherlock wondered if this was what it felt like to have your heart broken. To know that those he loved were in London, mourning his death, crying, in pain. His John, in pain. The very thought could bring him to his knees.
But it also gave him a reason to pursue Moriarty's web with a vengeance. Sherlock could never go back to his blogger with the snipers running free.
Sherlock watched his best friend fracture at the tombstone, touching the name "Sherlock Holmes" with a kind of reverence, the same reverence that had once accompanied "brilliant", "incredible", and "amazing".
But Sherlock noticed that John never said "goodbye". Not once. Not when John's voice was strong with conviction as he proclaimed his ongoing belief in a dead man. Not as he begged for a miracle. Not in the other trips to Sherlock's grave that Mycroft recorded and sent to Sherlock's mobile.
John only ever asked for Sherlock to return.
Finally, after years of separation, Sherlock was returning to Baker Street. John had never left, unable to leave Mrs. Hudson alone with the flat and unable to leave Sherlock's presence.
Mycroft and Molly had both warned him.
"He's still hurting, Sherlock. He could react dangerously," said Mycroft.
"He never stopped hoping. I don't think the poor man ever let you go, Sherlock. He clung to the idea that you'd somehow return and he never moved on. He could hug you, he might attack you, he might break down completely. Be careful, Sherlock," Molly had whispered.
But Sherlock didn't worry. Sherlock knew what John felt, or at least, he could imagine. It was the same hope that had sustained the detective for so many years. The hope of a reunion. The hope that, soon, they could go back to being flatmates, partners in crime-solving, and friends.
Sherlock walked up to the door of 221B -"Ah, Mr. Holmes." "Sherlock, please."- pushing open the door to the entry way -Sherlock and John, breathlessly laughing after a long run after, and then away from, a cab- walking up the stairs and, finally, collapsing onto the couch, -"Bored!".
John wasn't at the flat, he had been working more since Sherlock's death. So Sherlock was left to study the room, unable to discern a single difference in the room. There was less of a mess than usual and there weren't experiments cluttering the table or the refrigerator, but everything else was the same. None of Sherlock's things had been so much as moved an inch, although they had been cleaned.
Just standing in the room made Sherlock's eyes swim with images -John sitting and writing their latest case, John making tea, John forcing food on an unwilling, but secretly pleased Sherlock- and suddenly Sherlock was brought up short by a realization.
John wasn't just his best friend. John was what most people would call their family, or, more accurately, their heart and home. John was the tiny voice in the back of his head that told him, "This hotel is nice, sure, but it doesn't smell like tea and wool jumpers and adrenaline. There's no warm, understanding presence standing over your shoulder to tell you, 'Bit not good,' or 'Brilliant. Absolutely brilliant'. This place, however nice, lacks a John to make it home." And Sherlock understood now, that it wasn't a silly relationship that brought him to 221B Baker Street. It was that little voice in his head, constantly whispering, "You need to go home. Your heart is calling you."
In fact, Sherlock was so distracted that he didn't notice the uneven gait of his dear heart walking up the stairs until the door had opened and John had sighed in a heavy voice.
Immediately, Sherlock leapt to his feet and whirled to face his doctor.
"John," he breathed, unable to keep silent at the realization that this was real; he was home and he finally remembered what it was like to feel whole.
John stared, eyes wide and blank for a long, painful moment.
"John," Sherlock tried again, stepping forward and feeling an answering rush of joy at being that much closer to the older man.
"Sher-" John's voice broke halfway through the name. Tears threatened to spill over the soldier's eyelids as he took an answering step forward, sending another strong heartbeat full of life through the detectives veins. "But- you said goodbye- when you called, you acted like we'd never see each other again-," John was rambling in broken sentences, unable to organize his thoughts. Sherlock took another step forward, entirely too close for personal comfort, which meant John relaxed. Personal space had never existed between the two men and having space between them felt wrong. Sherlock spoke earnestly, his face open as he stared into John's careworn face.
"More the fool I. I'll always come home."