Sam was suspicious. He'd noticed that they would suddenly rush away from each other when he approached. Then it was the giggling from Dean's room, and the sweet wrappers in Dean's jean pockets. Sam sent Dean and Gabriel on a shopping trip so that he could get a sneak into his brothers room.
Once they'd left he quickly started searching for clues. He found sweet wrappers under the pillow, lots of empty lube bottles in the waste basket, and a fair number of used condoms. He ducked his head under the bed and found a box full of bright colured sex toys. With his face blood red, he pushed the box back under the bed, and took a moment to regain control of his gut.
"Sammy! We're back!" Dean shouted from the corridor.
"Shit!" Sam hissed, running to the cupboard and climbing in just as the door opened.
Sam watched through a crack as Gabriel walked in and put a black bag on the bed. Dean came in soon after.
"Sam say he was going out?" Dean asked in concern.
Gabriel smiled at him and pulled him close by the belt. "I'm sure he's fine, Sammy is a big boy. Stop stalling, I wanna play with our new toy."
Dean laughed softly and pulled Gabriel in for a hard kiss, the angel moaned and yanked Dean's shirt up. Dean allowed the angel to undress them both before they fell back onto the bed.
'Shit shit shit!' Was all that ran through Sam's mind in that moment, as he saw more of his brother than he ever wanted to.
Dean and Gabriel seemed so into it though and Sam found himself unable to look away or cover his ears. Dean arched against the angel and the angel held tightly to him in return. Sam had never seen anything like it, he wasn't sure if that was good or bad.
He watched as the new toy was revealed to be a bullet vibrator. He stared as Dean lubed the item and pressed it into the angels anus. The two moaned and Sam had to bite his fist to muffle his own noise. It was getting heated now and Sam could tell it was nearing and end. He put a hand down to squeeze his own erection, gasped as the pressure and the sight of a cum soaked Gabriel finished him.
He watched them kiss lazily in the last few pulses of sexual pleasure, his suspicions were correct and he was glad he got to see first hand.