The fingernails in the microwave aren't going anywhere, and he knows it. And Sherlock's public persona is a calculated mask that had been years in the making; no chance he would throw that over on account of an outbreak of sentiment.
If anything, John had thought Sherlock would perfect that uncaring veneer, give him fewer of those piercing stares that had had Scotland Yard whispering long before the day John drank himself into blubbering self-awareness. But Sherlock still gazes at him, unabashed, as if unaware that his feelings are visible to the world. As if his longings are still unsatisfied.