Sherlock survived on impulses. He made a living by thinking quickly and acting even more quickly. It was how he had gotten to where he was today. And it almost cost him the most important person in his life.

It had started simple enough. John had made a joke about the incident at the pool, and they had been lightly discussing the events of the night.

"You know, I never told you how stupid it was of you to tell me to run," Sherlock remarked dryly. "I had everything under control."

John snorted.

"I did!" Sherlock exclaimed indignantly. "I am not some helpless infant, needing to be saved by the great war hero John Watson," he added hotly.

There was a pause. "I didn't think of you as an infant," John said, his voice sounding shaky. "I saw someone I greatly cared about in danger. Any sane person would do the same."

The bite in his voice on the word "sane" stung Sherlock. He whipped his head around, ready to make a clever and vitriolic comment, but stopped short when he saw the look on John's face. There was pain, true pain behind his eyes.

"John, I-"

"Go to hell Sherlock," John snarled, rising from the couch and storming off.

Sherlock sat very very still for several moments. He then carefully rose from the couch and walked to the bathroom, grabbed something from the medicine cabinet, and walked up the stairs to John's room. He knocked on the door. No response. He knocked again.

"Sherlock, I told you to fuck off," John growled from inside.

"Actually, you told me to go to hell," Sherlock corrected automatically. He winced, realizing that this was absolutely the wrong thing to say at that moment. He gave up on niceties and barged into the room.

John was laying on his bed staring at the ceiling. "Okay, now I'm telling you to fuck off."

Sherlock stood in the doorway awkwardly. He took a deep breath.

"John, listen."

He wasn't cut off this time, which he took to be a good sign. He continued.

"I meant what I said. At the pool, I had things under control, I didn't need your help."

John let out a noise that sounded like a cross between a yelp and a growl. Sherlock held up his hand.

"Let me finish."

John was quiet again.

"I've never needed John Watson the war hero to save me. John Watson the civilian already saved me." He cleared his throat. "In more ways than he'll ever know."

He reached a shaky hand into the pocket of his coat and withdrew a small vial containing three white pills.

"Cyanide," he said softly, looking down at the vial. "I bought these the day before I met you." The world's only consulting detective chuckled to himself. "Why would anyone have wanted me for a flatmate? I was the tattered shreds of an ex heroin addict with a brain like a supercomputer. And now…" He looked up, locking eyes with his flatmate, who was now sitting up. "Well, I don't know exactly what I am. But I'm alive. And that is absolutely one hundred percent because of you."

The room was silent for what seemed like an eternity. Finally, John lifted himself on the bed. Sherlock braced himself, unsure of what would happen. John continued to shuffle across the room until they were merely inches away. Sherlock was amazed to see tears clouding the soldier's blue eyes.

"Where on earth did you get cyanide?" John asked quietly.

This was absolutely the last thing Sherlock expected to come out of John's mouth, and he couldn't help but laugh out loud.

"It's not funny!" John yelled, although the corners of his mouth twitched upwards. His exclamation was just the coercion his tears needed to leave his eyes and begin to stream down his cheeks. "It's not funny," he repeated quietly.

Seeing his doctor cry was too much for Sherlock. He allowed himself one more impulse, and this time around it was the correct thing to do. He delicately placed one hand on either side of John 's face and leaned in, brushing his own lips against Watson's. When John returned the kiss and wrapped his arms around Sherlock's neck, he saved the detective yet again. Sherlock Holmes would go on to save the world a dozen times over, but it was John Watson who was always there to save Sherlock.