So the story behind this is basically that I thought to myself what could've happened instead of the sex talk in 3x05.
Not that there's anything wrong with "That's why they invented masturbation", of course.
Urge
"I mean… have you ever had the urge to rip each other's clothes off and get dirty?" asked Kurt.
Blaine's mouth gaped open, but no sound came out. What could he say, "yes, Kurt, that's why almost every night I'm masturbating to the memory of the way your dick looked that one time when I walked in on you changing"? That's pretty much socially unacceptable.
So instead of saying that, he closed his mouth and pursed his lips, sitting down on the bed next to Kurt and taking his hand in his. "Sometimes," he whispered, and Kurt couldn't help it any longer- he leaned in and smashed their lips together, inhaling deeply and then opening his mouth to let Blaine's warm tongue in. They kept kissing until they were gasping for breath, and Blaine pulled away to nuzzle under Kurt's ear. His skin was flushed hot. "Do you, you know, get that urge?"
Kurt didn't reply, just grabbed the back of his neck and hoisted him up into a fierce kiss, all tongues and teeth and saliva, his other hand moving from Blaine's hold to grip forcefully on his bicep when Blaine moaned quietly and placed his hands on Kurt's hips.
When they broke apart for air again, Blaine pushed Kurt back onto the pillows and straddled him, none too careful about erections or any kind of personal space. He kissed Kurt sweetly and pulled away, then licked down his neck to that one beauty mark on his collarbone. Kurt gasped and his hips bucked up, and Blaine shuddered when he felt Kurt's painfully-obvious erection against his thigh.
Kurt tangled his long, pale fingers in Blaine's dark hair and pulled him up again. They looked at each other for a short moment, panting, their pupils dilated and their cheeks rosy, before bringing their lips together again. It was a long moment before Kurt whispered against Blaine's lips, "Now I really, really do."
"Huh?" replied Blaine dumbly, his mind fuzzy.
"I kinda have that urge right now."
"Oh."
Kurt grabbed two handfuls of Blaine's shirt, as if he really was about to rip Blaine's shirt off- but relaxed after a second and let go, smoothing the fabric with gentle palms. "Yeah."