It was James Moriarty who finally got Sherlock to see just how much Sherlock felt for John Watson.
The irony of it was not lost on Sherlock.
But the truth remained: illogical, irrational, incontrovertible. Sherlock had feelings and, what ever they may be, they were inexplicably intertwined with his flatmate. And now that the truth had been pointed out to him (horribly and violently pointed out to him) he found, much to his chagrin, that his mind had become fixated on attempting to rationalize and sort out once and for all what the hell to do with these so called 'feelings'.
And it was interfering with his work.
Sherlock caught himself staring at the Doctor at crime scenes when there was a perfectly interesting body he could be looking at. In the depths of a complex case when his mind was at its peak, he found images of John superimposing themselves on top of images of the victim. And he was even beginning to find himself strangely fascinated by John's person. By his facial expressions and body language. By the way he used his hands when he spoke. The way he still limped infinitesimally, not enough to impair his walk but enough that his gait was always recognizable to one with a well trained ear.
It was annoying and it impeded his ability to work and, since he did not seem to have any control over himself in the matter, the answer would have to come from John.
Sherlock came to a satisfactory conclusion and had just finished preliminary preparations for his plan when John came through the door with the shopping.
"You need to move out."