From Loosed Reins by AggressiveWhenStartled
This fic has some funny complications:
Why had it taken him so long to realize it? Sherlock had absolutely no sense of boundaries; it had been something he’d needed to learn with the same exacting care he learned anything he needed for the work. Still, he should have noticed sooner that John did have boundaries; in fact, John had amazingly wide boundaries. He simply never had them when Sherlock was the one testing them.
“I don’t want to sleep with you,” Sherlock told John sternly, glaring at him from the sofa.
John had just settled into his chair with a small plate of biscuits and a book, and barely glanced up. “I’ll cross shagging my insane flatmate off my to do list, then,” he replied, not really paying attention.
Sherlock frowned. “You aren’t taking me seriously,” he accused, sitting up.
It would be uncomfortable and boring, and as skilled as Sherlock was at lying, John would eventually realize and then get angry at Sherlock, which would be completely unfair, but entirely to be expected; John was unfortunately very much like normal people in certain ways. He would leave regardless of what Sherlock promised to do for him, and until then Sherlock would be bored, sore, and distantly irritated with the mess.
Sherlock still didn’t understand how “I will have sex with you even when I don’t want it because I want you to stay with me” was not seen as the selfless, giving gesture it clearly was, but he couldn’t change that. He could, however, change the direction of this train wreck waiting to happen.
“You should come with a warning label,” John told him, pointing an accusing finger. “Everyone and their dog knows you’re attractive. Celibate recluse monks in Tibet know you’re attractive. It comes with being insanely attractive. It doesn’t make me gay to notice it.”
“No, you’re entirely correct,” Sherlock agreed, “I should have been more clear. The part where you are clearly aroused when you notice my attractiveness is what makes you bisexual.”
John dropped his face into his hands, headache clearly blooming. “Fine. Whatever. I won’t have sex with you. Got it.”
“I’m simply not at all interested in sexual intercourse,” Sherlock explained, “and since you have sex with so many people it shouldn’t be much of a hardship to avoid having it with me.”
“Did you just call me a slag?” John asked, dazed.
Sherlock waved a hand at him, dismissive. “Of course not, I merely noted that you have many and varied sexual partners, and that you do not seem to be overly selective about them.”
“You just called me a slag,” John decided.
