After that, it became awkward. They avoided each other unless it had to do with hunting. Sam tried the trials, Cas released the angels. Sam was possessed by Gadreel, then he left.
"Keep going," Sam told Cas.
Cas removed the needle from Sam's head.
"No," Cas petted Sam's head gently.
Sam whimpered. I killed Kevin, Cas read Sam's thoughts, I should have died. Cas held Sam, knowing how it felt to not want to live.
"I failed, Cas," Sam said, "I always…"
Sam began to cry, from the pain of the needle as well as the pain of everything he'd done wrong. He shuddered in Cas's arms.
Dean was dead. Then, he disappeared. Sam and Cas teamed up, found the Book of the Damned. Charlie was killed. Sam is to blame, in his mind at least.
"Sam," Cas entered Sam's room late at night.
Sam wiped his tears.
"I'm sorry, Sam."
"What are you sorry for?"
"I should've kept Charlie from leaving," Cas said, "I didn't, and I'm sorry."
Sam hugged Cas.
"I missed you," Sam said.
"I was just here a few hours ago."
"That's not what I meant," Sam kissed Cas's neck.
Cas threaded his fingers through Sam's long, messy hair. Sam pulled Cas in closer.
"I love you," Sam whispered.
…

Sam moaned louder as Cas kept at work on him.
"Sam," Dean said as he walked down the hallway, "Keep it down in there."
Dean must've thought Sam was jerking off.
"Sorry," Sam said.
Sam pulled Cas's head in closer.
Cas lied in bed with Sam, stroking his hair.
"What are we going to tell Dean?" Sam wondered.
"I don't know," Cas said, "Nothing?"
"I don't want to hide things from him anymore," Sam sighed, "I just…don't know what he'll think."
"You mean, he doesn't know?"
Sam wrapped his arms around Cas.
"You're right," Cas said, "We'll figure it out in the morning."

When Dean looked into Sam's room the next morning, he felt two things: confusion that Sam was in bed with a guy, and anger at the thought of Cas porking his baby brother. He dragged Cas out of Sam's bed and held him by the shoulders.
"What did you do?" Dean demanded.
He was about half a second from strangling Cas.
"Huh?" Cas was confused, as he'd went to sleep along with Sam.
"What did you do to my brother?" Dean shouted.
"Dean," Sam said.
"Sam, what the hell is going on here?" Dean asked, trying to be calm.
Sam rubbed his eyes.
"It's not what you think," He said.
"Oh really?" Dean yelled, "Then why were you in bed with Cas?"
Sam opened his mouth to talk, but nothing came out. Instead, the look of absolute shame and humiliation spoke for him. Dean looked at his baby brother with sympathy.
"Something you want to tell me, Sammy?" Dean questioned calmly.
Worse than the demon blood. An ANGEL, Sam.
"I didn't think you would…accept me," Sam explained, scratching his head.
"Accept you?" Dean shouted, making Sam cringe, "You're my BROTHER!"
"I haven't known for very long, Dean," Sam said, "And Cas is an ANGEL, for God's sake! I was ashamed."
Dean hugged Sam tightly.
"Like I said," Dean started, "You're my brother. You don't have to be ashamed, okay?"
"Yeah. Thanks Dean."
"Anytime, Sammy."
Cas wanted to comfort Sam, but didn't want to piss off Dean any more.
"And you," Dean pointed and approached Cas, "If you hurt my brother, even once…"
Cas nodded.
"Understood."
Dean didn't need an angel blade to make that sound threatening.