He hasn't acted on it, but he has thought about it. On more than one occasion.
What it would be like to love Sherlock Holmes and was he even capible of doing such a thing.
John was far over his head on this one. He had felt this way for a long while now. Probably since their case in Baskerville. He was so angry at him that he couldn't see straight. He had every intention on telling Sherlock to "piss off" and swearing him out of his life forever. But later that night he knew that would never be possible.
He knew there would always be a part of him that would do anything for that god-forsaken wanker. A part of his heart and soul that Sherlock would fill and that would never change. John wanted to tell him. He wanted to tell the handsom consulting detective how he felt. The way he stays up until ungodly hours of the night playing his violin. How when he does an experiment he is focused to a level John had no idea existed. How badley he wished that what Sherlock focused on, was him. How he thinks about him practically every second of everyday. Okay, that was a lie. John watson thinks about Sherlock holmes at all times. He can't remember a time when he did something or thought about something that didn't involve the dark-haired man. Pretty much everything Sherlock does and say are things that John cannot get enough of, or live without. And John was surprizingly okay with this.
It was about 1 am when he finally turned the key in the lock at Baker Steet. He had just gotten home from drowning his "problems" at the pub when he heard faint voilin music. God, did sherlock know how to play. He loved it. Exspecually, after a case when Sherlock would play and John would sit on the sofa feeling deeply at peace as the music lulled him to sleep.
John sat down on the chair by the fire place with his eyes closed wanting to relax his mind to the music. A short while later as the music slowly fades in apartment 221B everything is thrown for a loop.
"I love you."
John's eyes flash open at what he just said. There was no way of taking it back or fixing it. Everything way out in the open. Not remotely close to the way John would have liked to reach this point.
" And I love you, John."
Sherlock is still facing the window with the violin resting under his chin when he takes in a deep breath and starts a new selection.