When the end comes, and it always comes first for Sherlock, it is a surprise. Regardless of where they are, sofabedfloorstairwell ("Be careful there for Mrs. Hudson's sake," John always says.) Sherlock finds that his orgasm is much like everything else in his life, rapid-fire and quick, brilliant spots of light on the insides of his eyelids. There is little warning of its nearness; just the sensation of John pressed against him, andinandoutandonanddevouring him. The rising push and pull makes Sherlock cry out, not just to John but to every sentient being that could understand the power of sex and love.
He would always come hard and unexpectedly taking John by surprise the first few times until the older man realized that Sherlock, who craved control and dominance, had no power over his own body's reactions. And empathetic John, gloriousamazingbeloved John, took Sherlock's inadequacies in stride with no more shaming a reaction than a bemused chuckle and a swipe at the semen dripping down his chin.
And Sherlock loved, ohhowheloved, when the end came. There were no words to describe it in the English language or any other that he knows. John gives his love away easily and Sherlock knows that he doesn't deserve if but he takestakestakes it anyway, greedily grasping for all that John has to give him.
He struggles to find a way to tell John his feelings but the sensation, which moments before was wondrous yet bearable, eclipses everything and his climax overtakes him and the words that he wished to say, lovelovelove, disappear in his mind and for a moment all is silent. The mysteries of the universe open up to him but Sherlock is too sated to care. The knowledge is enough.
And then John chuckles against his neck, amused again by Sherlock's quickness, but none of it matters because John knows how he even feels and he doesn't need the words voiced yet because in the end the love between the two men doesn't need explanations.