Dean, what happened to you?! Why are you acting differently all of a sudden?”
“Sammy, you know what I am, don’t you? There’s no stopping me now, so don’t even bother” Dean replied with a smug tone.
Sam didn’t want this to happen- ever. He knew something would change after Dean went to hell, but he expected nothing like this. One glimpse of Dean’s black eyes gave everything away- he became the very thing Sam hated the most. He thought it was his fault, that he thought he was strong enough so Dean didn’t need to protect him but now Sam felt betrayed and even more weak.
“Why, Dean? You became the very thing you used to hate!” Instead of answering him, Dean disappeared swiftly into thin air, leaving Sam to take in all of this alone. Castiel appeared a moment later only to be met with muffled crying located in the corner of the room. He turned around only to find Sam in a state which hurt him to see. As he walked over, Sam looked up as if he was glad to see a familiar face that had not turned their back on him.
“Sam, where is Dean? Is there something wrong which I missed?”
“I-I don’t even know anymore Cas, h-he’s changed!” Sam struggled to compose his words as the thoughts circled his mind and how tears continuously streamed down his face. Noticing he was in agony, Castiel bent down to his level and gently caressed his cheek. He didn’t enjoy seeing him in such a state and placed two fingers upon Sam’s forehead to put him to sleep. Whilst picking him up and carrying him to his bed, he thought about how he was going to find out what exactly happened to make Sam so distraught. After placing him on the bed, Castiel sat on the end and watched over him. He wanted Sam to not have to suffer all the time, yet he knew that would take a long time for everything to finally settle down.
Sam wanted his brother back, not some demonic impostor. Dean was in there and Sam was determined on bringing him back alongside with Castiel.
Dean knew that his brother would disagree with what he had become, yet it was necessary. He needed the power, and a part of him hated himself for taking it from Alastair. His brother was still with him, at least. Sam could handle himself- Dean was sure of it. But every time he had a spare moment, he was swarmed with regret ever since he turned into the diabolical creature Dean was now.
Every now and then Alastair would visit him; taunting him at every moment they had. Sometimes he regretted his offer, however the powers he gained were the best part of his agreement. Sam would have hated him if he said that he sold his soul to Alastair- which probably would have been for the best. Sure, Alastair had his charms, but Dean knew what lay underneath that demon and it terrified him. He didn’t want to hurt Sam, nor Alastair.
He taught him anew as Dean learnt the tools which Alastair used on him. It seemed insane, but Dean was always trying new things. Too many times he got caught up in the moment, and had to think of Sam to control himself. Alastair was driving him crazy; and he knew it. But somewhere deep inside him, Dean was enjoying himself a bit too much.