Uh...yeah. My first ever Sherlock fic, so I hope it turned out alright. This is a fill for this prompt on the BBC Sherlock Kink Meme: "Sherlock hates Anderson because he can't stand adulterers. After all, Sherlock's own husband goes away on tour of duty for years at a time, and neither of them would think of straying."

Fidelity

"From the state of Sally's knees and her complete lack of idiocy this morning, I can see she's finally grown a few brain cells. Or did your wife finally catch you at it?"

Sherlock watched Anderson's entire body flinch and didn't bother to hide his amusement and disdain when the forensic tech turned to face him. Anderson's face was scrunched up in anger and a small twist to his lips may have been guilt. There were dark circles under his eyes and he was moving more slowly than usual. Ah, so he did get caught, most likely slept either on someone's sofa or in a hotel...no, sofa. His brother's, the one with the Great Dane, there were dog hairs still clinging to his shirt. And if Sally's complete lack of concern were anything to go by, it wasn't with her that he'd been caught. He'd have to tell John the next time they skyped. He'd urged Sherlock to give Anderson and Donovan the benefit of the doubt, insisting that maybe Anderson just loved Sally more than his wife. Clearly not the case if he was sleeping with someone else barely a week after their last tryst.

"Go to hell, freak," Anderson snapped, slamming the lid of his kit shut. "It's none of your bloody business."

"Certainly not, but I am curious; do you have poor impulse control, or do you just dislike your wife?" He was genuinely intrigued by the whole mess, in a disdainful sort of way. Yes, he wanted to know why, but at the same time he didn't think the answer would really help him understand. Anderson lived with his wife, saw her on a daily basis, and still went out and had affairs with younger women. John was halfway around the world and Sherlock wouldn't see him in person for another four months, five days and nine hours, but he'd never felt the urge to find another warm body to sleep with.

Then again, before John the idea of sex with anyone had never interested him. The few times he'd experimented at uni had left him with the impression that sex was messy, irrational and boring. Sex with John was still messy and irrational, but it was John. The sex itself didn't interest Sherlock overmuch, but he did like cataloguing all of the ways John responded to his touch. And his own body's response to John's attentions were always pleasant and intriguing in their own way.

As for John, well, John was John. John was probably the most loyal man on the planet. The very thought of cheating on Sherlock had probably never occurred to him. Or if it had, he'd probably felt guilty just for thinking it and would most likely bludgeon the notion to death with the butt of his pistol.

While Sherlock supposed that not everyone could have his disinterest or John's unwavering fidelity, he still didn't understand how other people could so easily dismiss their vows without a second thought.

"Some of us are human, freak, we have needs," Anderson sneered. He picked up his case and strode towards the crime scene. Sherlock followed, sweeping along behind him like a malevolent shadow.

"So it is poor impulse control," Sherlock nodded to himself. That made sense. Of course Anderson wouldn't have the necessary focus to reign himself in, given how easily he leapt to conclusions at crime scenes before examining the evidence.

Anderson huffed and walked faster, fuming. Maybe if he ignored the psychopath he'd leave him alone and find someone else to pester.

"Lestrade," Sherlock nodded to the DI as he slipped under the caution tape. "You said it was gruesome?" His eyes were bright with glee and anticipation at the very prospect. If it was really grisly and complicated, he wouldn't think about counting down the minutes until he got to talk to John. "Then again, your usual definition of gruesome is horrendously dull and tedious."

Lestrade looked torn between resigned and amused. "Considering that two of my constables had to leave the room to throw up, I think it's gruesome enough even for you." He gestured for Sherlock to follow him into the building.

"That's not terribly reassuring since your constables don't have the wit God gave tree sloths. I imagine papercuts are enough to turn their stomachs."

"I take it you haven't heard from John, then?" Lestrade rolled his eyes. Sherlock was always a bit nastier when John had been out of contact for a week or more.

"We have a skype date tomorrow night." Sherlock ducked his head to hide a delighted smile that had nothing to do with the prospect of a case.

Anderson made a disgusted sound as he fell in step behind them. "You must have brainwashed the poor bastard. Stockholm syndrome or something."

Sherlock glanced back at the forensic tech. "Careful with the multi-syllable words, Anderson. You might strain something. In fact, don't even bother with the single-syllable words, either. Every time you open your mouth I can feel my brain cells dying."

"It's the only explanation," Anderson continued, bristling. "He ran off to the desert to get away from you, and even that wasn't far enough. If he has any brains at all he won't come back."

Lestrade paused, trying to decide if he should interfere before he had to arrest Sherlock for assaulting an officer of the law, when Sherlock started laughing. Not the crazed, maniacal laughter he indulged in when he was being clever or cutting, but the surprised genuinely amused kind. As though Anderson had told a funny joke without meaning to.

"Tell me, Anderson, do you always project your insecurities onto other people or is that truly the best jibe you could manage? Of course it was." Sherlock moved a hand up to the collar of his coat and slid a thin silver chain out from under his shirt. There was a gold ring dangling from it, freshly polished and glinting in the light of the streetlamps. There was something off about it, and when Lestrade peered closer, he noted the size. It was a size too large for Sherlock's slim fingers, but why would he-...Oh.

Lestrade couldn't help the amusement that showed on his face. Who'd have thought that Sherlock "I'm-a-high-functioning-sociopath" Holmes would do something as sentimental as this? He had no doubt that somewhere in the Afghan desert Captain John Watson was dashing about with a gold ring that was too small for him dangling around his neck.

Anderson gaped, looking from the ring, to Sherlock's face, to Lestrade and back again, as though waiting for someone to reveal the joke. Sherlock smirked, triumphant, and tucked the gold band back under his collar before he swept away towards the crime scene.