The fourth reason Sherlock's learned that John has sex with him is that John is sorry. Sherlock knows John's probably lived quite a bit of his life thinking everything wrong has been his fault, and if sex is something John's good at then it's sex that he offers someone to forgive him.
Sherlock learned this fact six months into their relationship, just after their first big fight. Sure, they'd fought before. Little tiffs never meant anything before this fight.
Sherlock can't exactly remember why they fought (yes he does, it's because he didn't solve a case and let a young boy die, John was so upset with him and Sherlock only cared that he didn't solve the case) and John left. He didn't leave, he obviously came back, but he did shout a lot of choice words like:
"Honestly, Sherlock, I don't know what I ever see in you because you are the worst human I've ever met in my life!" and:
"I'm leaving and I may or may not come back, Sherlock, because I can't handle this anymore I really can't!"
So John left and went to Sarah's, which was just the icing on the cake for Sherlock. John could have gone anywhere in London, he could have gone to his sister's, he could have gone to his ex-sister-in-law's, he could have gone to Mycroft's, even, but no he ended up at Sarah's and Sherlock was pissed.
What made it worse was that John didn't return for two days. When he got home Sherlock knew he went and bought new clothes just so he didn't have to return home, and that broke Sherlock's heart more.
When John finally did return, Sherlock was laying on the floor of the living room surrounded by books and random items that belong to John. He wasn't wearing pants but instead wearing underwear and one of John's shirts. John silently stepped into the flat and took his coat off.
"Come to collect your things?" Sherlock asks without lifting his arms from their position covering his face.
"No."
"Oh," Sherlock lets the silence settle in to see what John does next. When John doesn't move, Sherlock asks, "Where've you been?"
"You know where I've been."
"Sarah's was nice, then? Nice enough to stay two days."
"That's not…" John sighs, "That's not why I stayed there, not because it's nice."
"But it was nice."
"Sherlock, that's not the point. I didn't come home to tell you Sarah's is nice or not nice."
Sherlock finally looks up at John with tired eyes. "Home?" he asks, "Is this still where you live?"
John kneels down next to Sherlock's hip. "Sherlock I came home to tell you that I'm sorry."
"Oh?" Sherlock asks, sitting up.
John sits cross legged next to Sherlock's hip and facing Sherlock. He reaches over to touch Sherlock's face, Sherlock winces. "I'm so sorry, baby, I didn't mean…I could never…you're not the worst human I've ever met…" John can't quite find the words because Sherlock is staring at him like he so does not care. John continues, "Sherlock please don't look at me like that, ok? I'm so sorry for what I said and that I yelled at you." John leans in and wraps his arms around Sherlock. Sherlock doesn't move. "I could never leave you. I love you so much." John pulls away and takes Sherlock's face in his hands. Sherlock looks at John and sees that John is crying before John's lips are on his. Sherlock doesn't touch John or even close his eyes at first, and John knows because John starts to cry a little bit more, so Sherlock closes his eyes, opens his mouth, and wraps his arms around John.
After a few minutes they migrate to their bed and John gently lays Sherlock down before lying on top of him and beginning to feel in Sherlock's underwear.
"I'm so sorry, my love, so sorry," John whispers in Sherlock's ear.
Sherlock tugs John's face off him and says the first words he has said since John shut him up and apologized, "Don't leave me, John."
John pulls his hand out of Sherlock's underwear and instead wraps his arms around Sherlock's waist. "Never, Sherlock, I'll never leave you. I'm so sorry." He kisses Sherlock again and a while later Sherlock fully catalogues "I'm sorry," as a reason for John's sex.
Sherlock doesn't get much I'm sorry sex because John doesn't make him angry that often, but Sherlock does sure as hell give a lot of I'm sorry sex.
The fifth reason John has sex with Sherlock might be Sherlock's personal favorite (if he hasn't chose a favorite yet). The fifth reason for sex is when John's in the shower in the mornings, Sherlock may or may not wake up a little bit randy and a little bit hard and he likes to invade John's shower time. Sometimes John will half-heartedly protest by saying he has to get to work soon and he's already late, but all in all he welcomes his boyfriend with welcome, wet, soap soaked arms.
"Sherlock, what're you doin'?" John asks with a smile on his face as Sherlock steps in and takes the soap from him.
Sherlock smiles, his face still sleepy and his eyes still half shut, and honestly John doesn't love a site from Sherlock more. There's something about the detective just waking up that gets John in the mood, it's probably that John sees Sherlock fresh in the morning so rarely that it's a site he has to soak up. Sherlock covers himself with soap, letting his skin gets silky and smooth with water before putting the soap down and pressing his body against John's.
There's something about two soap slicked erections rubbing against each other and Sherlock and John love it. Pumping against each other in the shower is a quick way to get them both moaning and groaning in that small steam filled shower, but today Sherlock wants more. He takes John's shoulders and presses John against the wall, the cool tiles touching his erection and making him moan instantly.
"I woke up," Sherlock starts as he lubes his fingers and gently presses one into John, "And I had to have you before you go to work."
John moans, "Lucky for me I got up earlier than usual."
Sherlock smirks. "Like that would have stopped me."
John smiles then feels Sherlock push another finger into him and the smile fades into a mouth opened wide moan. "Oh, baby," John babbles. Sherlock curls his fingers slightly at the end and John groans breathlessly, "Just like that."
"I dreamt about you last night," Sherlock states, "I dreamt we were fucking in the back of Lestrade's police car."
"How…mmmmmmm," John pauses to moan and catch his breath as Sherlock adds a third finger, "How was it?"
"It was great," Sherlock bites his lips and presses his forehead against the back of John's head, watching himself stretch John. "I was leaning back, my head against the window, and you were riding me," he pauses for John to moan, then continues, "Didn't get off, though, I woke up and came in here."
"Lucky me, then," John reaches around his own head and grabs Sherlock by his hair. "Stop playing and fuck me, Sherlock."
Sherlock doesn't have to be told twice, he gently pulls his fingers out, lubes his cock, and sinks in. He slowly pushes all the way in, so far in that his smooth, watery chest in pressed against John's smooth, watery back. The water makes it so easy for Sherlock to move and grind against John and so easy for John to grind against the wall. Sherlock takes John's hands in his and hold them against the wall above John's head. John presses more against the wall and Sherlock more against him, his hips rocking rhythmically back and forth into John.
"Fuck, John…" Sherlock mumbles then moans. He lets one of John's hands go, which goes straight to Sherlock's hair, and Sherlock's free hand snakes its way down John's belly to his erection.
"Oh, god," John chants, "God, that's…Sherlock that's…" Sherlock gives John one hard thrust and John moans so loud it's almost a scream.
Sherlock keeps up the deep, hard thrusts and soon they're taking turns yelling moans and profanities at each other. Finally John comes into Sherlock's hand and Sherlock a few minutes later, Sherlock comes into John. Sherlock rests his head on John's shoulder as he watches himself pull out of John, he chokes a moan. He runs his hands over John's wet body and leans against the wall next to John.
"Sherlock," John says, still pressed against the wall, "That was—"
"I know," Sherlock says with a proud smile.
"Thinking about how amazing that was," John pants, "Makes me want to go again."
"Just give me a minute, ok? Then I'm all yours."
John laughs, "Funny, but I've got to go to work."
Sherlock smiles, "No you don't. I called Sarah, you're not going in today."
"What? Why?" John demands, almost angry sounding.
Sherlock smiles as wide as he can and gives John a quick kiss. "Happy Anniversary," he says before exiting the shower.
John stands under the water for a minute longer just shocked by Sherlock's action. He finally gets out and Sherlock is in the kitchen waiting for John to make him breakfast. "It's my anniversary, too," he claims when John says Sherlock should make him breakfast.
Later that day Sherlock finds that the sixth reason John has lots of sex with him is because anniversary, and after that Sherlock makes up anniversaries for everything (the day they got together, the first day they had sex, the day they met, the day Sherlock came back from the dead, the day Sherlock died (John does not condone that one)).
Sherlock will probably never tell John about this study because John will probably thinks it's disturbing, but Sherlock likes to keep it as a friendly reminder that if John's feeling certainly loving, or they're coming off a long case, or John's cold, or John's sorry, or John's being super sexy in the shower, well then Sherlock will definitely be getting a piece of that little man and Sherlock loves that.
*Everyone always needs a little bit of porn, right? Written because I'm bored. Thanks for reading! Please review. : )