Sherlock was half in the door and half out of it, clinging to the frame, reeling from his recent contact with John's fist. The only thought running through John's head continued to be "What the hell?"
Studying the look of utter confusion on Sherlock's face, John had a startling epiphany. The man had seriously thought he would be happy to see him. Happy... happy that this man who had killed himself right in front of him... in front of Ihim/I, mind you: a doctor who had been helpless to save his comrades-in-arms, a colleague who had been at Sherlock's side through thick and thin, a warrior who had bloody well killed a man to save Sherlock from... another, slightly different, form of suicide (How had he missed that aspect before?). And Sherlock had not only jumped, but had done it as he looked up from the street, powerless. While talking to him. And even if that was somehow required of John, for Sherlock to have faked his death and for him to have been a witness to it...he had not said a word, wrote a letter, sent a secret code or something, Ianything/I, ...nothing- until showing up in a melodramatic heap on his doorstep. Here he was, strolling back into his life, expecting a joyous reception.
As Sherlock stood there searching for words, John's mind filled in the missing dialogue:
"I am not dead. I am, in fact, very much alive. Why shouldn't that make you happy?"
"You selfish git! Is that all the depth your brilliant brain can conjure up concerning human emotion? 'You thought I was dead! I'm alive! Be happy?'"
"Why shouldn't you be happy, John? I had a brilliant plan. Fooled everyone. Let me tell you how I did it..."
John scowled. Now he had to try to explain to the said-same selfish git all that he had gone through... all the pain and betrayal. That was Sherlock all over. But instead of seeing a gloating megalomaniac staring at him from the doorframe, he saw a man with tears running down his face.
"That jump was the happiest day of my life, John. It was a glorious moment. I planned it out so carefully. But it got so much better, John... so much better! I'm sorry John, it's just that seeing you again is... it's so sad. I don't know if I can handle it. Forgive me for coming home. Forgive me, but I just had to."
John was stunned. Everything about this was wrong. The words. The cadence. His voice itself. How deathly ill he looked in the fluorescent light of the flat. Everything.
"But, I know that the last few years have been very happy ones for you, too. I've been watching you. The loneliness that you feel. The anger at me. I've been enjoying myself, too...taking out Moriarty's team. I've gone without food for days at a time and had to sleep out on the snowy mountainside. I've never felt more elated in my life, but I know life is not just endless joy, it is also sorrow...now that I'm back."
Nothing he said had made sense. Sherlock's handling of emotion had always been a bit, well, perverse, but John knew he must be in some form of shock... and here he had just decked a man who had clearly been traumatised, perhaps for years.