John almost skipped home. He'd managed to convince a colleague to come in an hour early, he could barely keep still with his last few patients. He was going to do it. He was going to see if, even after embarrassing the poor man half to death last night, he could convince Greg that he'd changed his mind. Because who cares what label you use or don't use. That kiss was amazing. He wanted more. And it was Greg, so smart, self-effacing, funny. He'd been such an antidote to Sherlock and such a good friend to John. He didn't just want to sleep with him. He wanted to be with him. Date him. He wanted to sit with him in front of the TV and laugh at a stupid movie and snog like teenagers.

John grinned to himself as he headed up the stairs to the flat, so wrapped up in his own internal monologue that he didn't hear the noises until he opened the flat door. It sounded like... but Sherlock wouldn't be... Sherlock didn't...

"Oh God, Greg let me come!"

"No, not yet..."

John felt his stomach drop away, those two voices, so familiar but so different to how he'd heard them ever before. Sherlock was almost whining, his normally deep baritone high with need, and Greg's voice was a deep, growling command. John would have dropped to his knees with a word if Greg told him to in that voice.

He kept walking, on autopilot, towards Sherlock's bedroom, the door was ajar a little, the two men clearly weren't expecting to be interrupted. John slid along one side of the corridor so he couldn't be seen and carefully looked through the small gap. What he saw took his breath away. Sherlock was on his back, his leg's spread wide and hands gripping hard on the bedframe as Greg pounded into him. Greg was gripping Sherlock's hips with both hands, holding him still so he could thrust deep and hard into Sherlock. They were both covered in a fine film of sweat, each muscle on their bodies in sharp relief, taut and shaking with need. John found his hand palming at his cock through his trousers, God he was rock hard and aching already. He'd gone from straight vanilla John Watson to a gay voyeur in less that 24 hours. That was wrong and twisted and so very fucking hot at the same time.

"Greg, oh God!"

"Tell me what you want Sherlock"

"I want... I want..."

Greg growled. "Tell me, tell me or you don't get it."

"I want you to touch me, I want your hand on my cock, I want to come."

John could imagine Greg's grin rather than see it. John surrendered to the inevitable and popped the button on his trousers to wrap his hand round his hot, hard cock, already dotting his boxers with pre come.

"Then beg for it."

"What?"

"You heard what I said..."

Greg slowed his thrusts right down.

"Beg for it. Beg me to let you come."

"No!"

"Why so shy Sherlock, you know you want to."

Greg leaned over Sherlock, his belly rubbing against Sherlock's cock, giving him the friction he craved, but clearly not enough if Sherlock's groans were anything to go by. Greg dropped his mouth to Sherlock's ear, John might not have heard if he hadn't been so close, so close to both of them.

"Because you know what, I don't even think you need my hand on your prick to get you off, you're so close already aren't you, I think that you could come with just me coming in your arse." John gasped and started fisting his cock faster and tighter "I think you could, I know just how to make you, you just have to say please."

Sherlock made a noise that was almost a scream "Please! Please please please! Please come inside me, fill me Greg, please, let me come."

This time Greg moaned and leant back, adjusting the angle, speeding up this thrusts and adding a roll to his hips that was clearly hitting Sherlock's prostate dead on every time.

"Oh God Sherlock, yes, oh I love you like this begging, aching needing me... tell me what you want."

"I want to feel you come inside me, please, please..."

"Oh yes, yes you do don't you, that's so good, you're so hot, fuck Sherlock I'm going to come, I'm going to fill you, come for me!" Greg thrust once more deep inside Sherlock then threw his head back and roared, Sherlock screamed underneath him, shooting thick white ropes of come all over Greg's chest and John came with a shudder all over his hand.