“How could you do that?” Sam asked brokenly, staring down at his knees. He knew if he looked up he'd see the look on Castiel's face and it would break him even further.
“I thought it would help, that he would help,” Castiel replied, quiet and apologetic.
“Do you know how difficult it was for me? To accept responsibility for letting him out and to throw him back in? I still have nightmares about drowning in demon blood. I know you know that, I won't let you touch me after them.”
“Sam-” Castiel started, only to be cut off by Sam jumping up in anger.
“No! I spent centuries in that pit in penance. The things he did to me...and after I finally got out I thought that he was behind me, a nightmare to be repressed,” Sam spit out. He swiped at the tears sliding down his cheeks and went on, voice raising with every word. “Yeah, I thought he could help us with Amara but I also thought my visions were from God. Instead, they were just a trick to let him out. And even though I knew he was still powerful enough to help, I told him no. I denied him my body and his freedom. I felt strong for once and I was proud of myself. But then you- you-”
“Sam, please!” Castiel begged, not wanting to hear the actual words.
“You threw that away,” Sam said, his voice quiet and dead. “My biggest sacrifice, my one redemption, and you just threw it away like it was nothing.”
“I know!” Castiel shouted. “I know I did! But I was caught in the moment and I thought he would help and I was tired of being useless.”
“You're never useless, Cas,” Sam denied, shaking his head. He moved to the door of their bedroom and opened it, preparing to leave. “But here's the kicker. I would love you even if you were. Even if you didn't have an ounce of power or training or what have you. But if you don't know that by now, then I guess you don't know me at all.”
The door closed behind him with an air of finality.