Contrary to popular belief, Sherlock did possess the ability to feel emotions – he just chose not to invest in them.
However, at this moment in time, as he looked at the hung-over man he had missed for many months, he couldn't control it. Tears ran relentlessly down Sherlock's cheeks and he found no way to stop them.
"You see..." he choked out, desperate to explain to John why he had done what he had, but for the first time he was unable to find the words to start. All he really wanted was for him and John to go back to their friendship before Jim Moriarty had invaded their lives, a wish that went so much against logic that Sherlock grew angry with himself. Why was he being so pathetic?
"Sherlock..." John's voice, so full of concern and pity, sent an even larger stab of annoyance through Sherlock; he didn't want John to see him like this, weak and vulnerable. Sherlock took a deep, steadying breath and delved into his explanation.
"Moriarty was clever, almost too clever. He manipulated the media, the public, everyone, into believing I was a fraud. He nearly managed to trick you..."
"He did not!" John muttered.
"...He was clearly out to get me and bring me down, kill me even. I easily figured this out, but how to avoid it? That was much more difficult. I knew he wasn't going to kill me personally, so I knew he'd make me kill myself. It's his style, big and dramatic; Confessed Fraud Commits Suicide. A perfect end to a perfect tale. So I planned with Molly and Mycroft to have me pretend to kill myself by jumping off the hospital roof and into a truck filled with various items to break my fall. I had two squash balls under my arms to stop the pulse in my wrists, and I had the help of an aspiring makeup artist to cover my head with fake blood while you were hit by that bike. She did an okay job, but surely even you could have realized that the blood was flowing in the wrong way?"
"Clearly not..."
"You're a doctor, for crying out loud, John! Never mind. Anyway, after I faked my death I had to stay with Molly. It was torture, believe me."
"Really? You think staying with Molly was torture while I was here, thinking you were dead? And you didn't even explain why you did it." John's voice rose heatedly.
"I know..." Sherlock replied. He didn't want to explain, relive the idea that John's death had come so close. However, John deserved to know why. Even Sherlock knew how unfair it was not to tell him.
"As you're aware, Moriarty had hired assassins. He instructed three of these assassins to kill you, Mrs Hudson and Lestrade unless I admitted I was a fraud and killed myself. Believe me, though, John: I am not a fraud, and I did not want to hurt you. I wanted to keep you alive."
There was silence as Sherlock watched the comprehension appear on John's face.
The silence lasted for a long time. There was nothing to say anymore. Sherlock had explained, and now all he could do was wait for John to say something, to show that he understood, to show he still wanted him around...
"Get out." John's voice was hard and cold. It did not quiver, it did not break; it was emotionless.
Sherlock looked at John's face, trying to work out what was going on. Deducing crimes was simple, but human emotion... That was another thing.
"Please understand, John," Sherlock pleaded, feeling idiotic at the sound of desperation in his voice.
"I understand."
"Believe me, John."
"I do. I believe in you, Sherlock. Now leave, I need to be alone."