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In the beginning Dean had to take several blood shots a day, sometimes even hourly, to stay human. He hated it, but it was necessary. They found that out rather unpleasantly, but Sam didn't make the same mistake twice. It was a hard struggle, and the Mark of Cain didn't really help either, but Dean was determined to win over his demonic side. It usually started with a dizzy feeling, his hands getting cold and clammy, his vision blurring in and out of focus. His voice would get deeper, raspier, animal-like. Sam noticed too late, so he and Cas had to look for Dean the demon, strap him to the chair in the dungeon and pump his veins full of sanctified human blood. The process was just as painful as the first time, but Dean was thankful for Sam and Cas trying so hard to keep him human, after everything he'd done to them.
The first few weeks were extremely emotional, after months of feeling almost nothing at all. He broke down crying more than once a day, had panic attacks or locked himself in his rooms for days in a row. Cas always made sure he got his blood injections though. Dean was very thankful, but he couldn't put his thoughts into words, so he kept silent most of the time. Sam and Cas were patient. As long as the cure worked, they would wait for however long Dean needed to fully recover. He already needed less injections a week after he first fought his demons, and by now he injected himself four times a day, before each meal. He was less moody and more talkative, and if he had a good day Sam could even see through the broken, sometimes suicidal façade and catch a glimpse of his big brother, how he used to be before he got the Mark of Cain. Dean noticed, too, and sometimes he thought that, maybe, the Mark was beginning to fade. It didn't, of course, and Dean knew it was impossible. It was probably just wishful thinking.
Sam was drunk on more evenings than he wasn't. Dean could relate, but after being turned into the demon he couldn't stand it any more. He hated anything that clouded his mind, and as much as he would've loved to numb all the overwhelming emotions, he didn't dare take a sip. The months of Dean's absence had been hell for Sam, and Dean felt a sharp sting of pain right in his chest, where he supposed his heart was, when he saw how worn out Sam's expression was, how little passion he had left for anything he tried to accomplish, knowing that was his doing. Sam spent most days in the library, distracting himself with the stories that the first Men of Letters had written down. Dean tried to be happy when Sam was around, in hope it would lift his spirits as well. But Sam knew Dean too well to fall for his tricks. After some weeks of isolation Sam was almost himself again. His cheeks were still hollower than they were supposed to be in Dean's qualified opinion, and the dark circles under his eyes just wouldn't fade, but Dean sensed that Sam was recovering. He just did it in his own way, and as long as it worked Dean was okay with it.
Cas began to get stronger as well, The stolen grace healed him, but Cas hated it. He couldn't stand using up another angel's juice of life. After all, it was his own fault his grace had been taken from him by Metatron. Now he had to deal with the consequences. Still, he had to admit that having his angel powers back, even if it was only temporarily, had it's benefits. He didn't use it too much, though. He knew it would be gone faster than he wished, and since they didn't go hunting at the moment he didn't need it to smite demons or heal his friends.
Cas made sure to keep close to Dean. Whenever he could feel a shift in his mood, his voice changing, his muscles trembling, he would zap to the blood tank, get out a shot and zapped back to Dean to inject him. He knew it would break his heart to lose his human again, even if he could never understand just how much he meant to Cas.
***
Dean's condition changed again when he began seeing things. It started with a fever, and he had to stay in bed most of the time. Cas tended to him, he fed him and made him tea and injected the blood. When he was asleep, Dean had the strangest dreams. They were memories, of him and Sam and Cas, but also memories that weren't his. He was in a car with a dark-haired, blue-eyed woman. Dean knew instinctively that she was an angel. They sat in silence, and then the scene changed. He was in heaven, only this wasn't his heaven. He felt angry, but also full of remorse. All around him lay countless corpses, each with a huge pair of wings burned into the ground around them. The scene shifted again, and he watched himself raking leaves in the backyard.
“Dean? Are you okay, Dean? Do you need an injection?” a familiar voice asked. Dean was forced to consciousness, and when he opened his eyes the only thing he could see was blue.
“What the hell, Cas!” he said, his voice no more than a crackly whisper. He cleared his throat, but it didn't get better. His heart hammered inside his chest and he was bathed in sweat.
“I came to look after you.” Cas explained. “I had a strange feeling, like something was wrong. You were asleep, but it seems you had a terrible night mare.”
“What, uh, yeah I did. Thanks for waking me up, man.” Dean said, very aware of the closeness between his and Cas' face. “Um, do you mind?” he asked, propping himself up on his elbows, which made Cas stand up straight, suddenly awkward.
“I'm sorry.”
He stood in silence for some time, while Dean tried to remember what his dream had been about, but he failed. All he could think about was how close his face had been to Cas', how close their lips were... Stop this! He demanded himself. Cas is a celestial being. He could never like someone who turned themselves into a demon. These thoughts had been plaguing him ever since he was human again. Before he had turned into a demon, there might have been a tiny chance that someone like Cas could actually fall in love with someone like him. He got his hopes up especially high when Cas became human, but fate kept pulling them apart. In his mind he had played it over and over. There was just no way this could work out. By becoming a demon he had closed every door there might have been forever. And now that Cas had some grace back he would surely have better things to do than to start a relationship with a miserable, broken human being. Dean looked at Cas and caught him staring into his direction. It was dark, but Dean could see that Cas was blushing, as was he. Cas cleared his throat. “I guess I'll leave. Sleep well, Dean. Call me if you need anything.” and he disappeared. It took Dean a long time to fall asleep again, and this time he didn't have any dreams.
***
Dean woke up to the smell of pancakes. He opened one eye, curious where the smell came from. Standing in his room was Cas, who held a plate with pancakes on it. He already wore a suit and his trench coat, although he was going to stay at the bunker all day.
“I thought maybe you wanted some breakfast. I'm sorry, it was a stupid idea.” Cas turned around to leave the room.
“No, wait Cas. Wow, pancakes. That's perfect. Thanks!” Dean sat up against the wall. He scooted aside and patted on the space that was now empty next to him. Cas took a hesitant step forward, and then he looked into Dean's eyes that shone in a bright green, with a few golden spots of reflecting light. He smiled an encouraging half-smile at Cas and wiggled with his eyebrows. This random motion gave Cas the guts to sit down next to Dean and offer him the first pancake. Dean gladly took it and almost swallowed it in one bite. “That's delicious!” he said, but Cas couldn't understand what Dean was trying to tell him because his mouth was full of pancake. They ate in silence after that. When all pancakes were eaten Cas took the plate and left Dean's bedroom. He got up and dressed, and after some consideration decided to go looking for Sam. He found him in the bathroom, hugging the toilet bowl. Sam made a sound as if he was going to throw up, but he didn't. “Rough night, eh?” Dean greeted his little brother. Sam just groaned in response. “Need some water?” A confirming groan escaped Sam's lips, so Dean left to fetch a glass and some water from the kitchen. When he returned to the bathroom Sam sat on the floor, leaning his back on the wall with his long legs stretched out in front of him. He looked miserable. “You know, Dean, I should be the one taking care of you, not the other way around.” he said weakly. “Bullshit.” Dean handed him the glass and watched appreciative as Sam downed the water in one go. “You need more?” Dean asked. Sam nodded and gave him the glass. This time Dean didn't go all the way to the kitchen, but instead filled it up at the tap in the bathroom. “Here you go.” Dean felt like he had lots to make up to Sam. After all, it was his fault that Sam was in the condition that he was in. It was him who had abandoned him, who had threatened to kill him more than once and almost succeeded, if it hadn't been for Cas. Cas, who had pulled him out of hell. Who had sacrificed so much for him. Who died for him, over and over again. Who fell for him and who came back for him, even after Dean's worst downfall. He felt a wave of warmth flow over him, which was followed by a tingling, bubbly sensation in his tummy. As if Sam had sensed it he brought the topic up. “What's up with those visions you've been having?” Dean stiffened at the topic. The visions hadn't stopped since the night he had woken up to Cas being only inches from his face, but there was more to it. He didn't only see things, he also felt them. The memory of that incident made his heart stumble, missing a beat and then taking up the pace, pumping blood through his body that warmed each cell of him. He felt incredibly human, and he liked it. “Same as last time you asked.” Dean wasn't particularly eager to talk about it. The visions were mostly of him and Cas, and Dean didn't feel comfortable talking about it with Sam. But there was nobody else he could talk to. Cas was no option, since the vision were often very … intimate. And he somehow had a feeling that maybe Cas had more to do with it than he was consciously willing to admit.
***
Curiosity always won him over. There was nothing Sam could do about it, it was in his nature. He had to find out what Dean's vision were about. Sam spent every day at the library, reading everything about dreams and memories and visions and basically anything like it. And there was nothing. He felt helpless. Up to this point, books had always helped him to solve his problems. On the other hand, there had never been a case like Dean's. Out of desperation Sam decided to go for the last option he had: talking with Castiel. Finding him was no problem, he usually lingered in the living room. It was rather how to begin the conversation about his brother that was a worry to him. “Cas? You up to something?” he began awkwardly. “No, Sam. Do you need something?” “Yes, your opinion on a matter concerning Dean.” Cas froze. His shoulders stiffened and he took a deep breath. “What about him?” “Well, he.. he's been having this sort of visions since he's human again. He sees things or dreams about them. It's mostly memories, but they don't seem to be his own. He's always present, but the perspective is not the way he remembers it.” Cas sat still for a moment, processing the information. “When did these visions begin?” “Since he regularly injects - … wait a minute. I'll be right back, Cas!” Sam turned around and ran towards the blood tank as fast as he could. He quickly looked through the blood containers. How the hell hadn't he noticed before? Sam almost laughed about his own obliviousness, but there were still some things that needed explaining. He picked up an empty container and went back to see Cas again, who had barely moved from his place on the couch. “So did you find something?” “Indeed I did.” Sam held up the blood container. “What about it?” “Read the label, you moron. It says Clarence Novak on this and every other container. You and Dean are the same blood type. We have been injecting him your blood for weeks.” Realisation dawned upon Cas' face. “So you're saying... Dean has insight to my memories?” “Apparently, yes.” Sam confirmed. “And is it only memories … or emotions as well?” “I have no clue. He doesn't talk about it a lot. But why is there so much of you blood anyway?” “I figure I'l need to explain that. When I fell I was alone. I was broken. And I was homeless. I'm sure you remember the church where I found shelter? They handed out hot soup for us in exchange for simple work. But it didn't feel right to me, taking so much and giving so little. So when the Red Cross organized a blood donation at the church I volunteered. They were sceptical about my blood at first, because many of the homeless took drugs. But my blood was clean, so they were happy to let me donate. I did so every time they were there. And now it seems that it has indeed saved a life.” “Wow, Cas. I never knew. You saved my brother.” Sam pulled Cas into a tight hug. Cas continued talking. “At that time I still had a tiny bit of grace left inside of me. If it was in my blood, then...” “Then maybe the blood didn't work because it was sanctified, but because it was intermixed with grace! Your grace annihilated the demon juice in Dean's body. You saved him.” Sam was forever grateful to Cas. Because of him he had his big brother back. He hugged him again, and then began to wonder. “So maybe the connection isn't because of the blood, but because of the grace. Dean now carries a little of your grace with him, possibly forever. That means you will always be connected.” he reasoned.
***
A month later Dean still had the visions. They came more frequently, and were more intense than before. Sam hadn't told Dean about his theory, but Dean had done his own research. He was fairly sure that Cas wasn't as innocent as he made it look. After finding out about the blood Dean tried out several things. He called it science. One time he went into Cas' room right after showering, only a towel around his waist. He could almost feel the trace of Cas' eyes as they scanned his naked upper body, and he could most definitely feel the blood rushing into his ears. At the same time he saw Cas' ears blushing. He smiled, said he'd forgotten what he wanted to ask, and went to his room where he danced a little happy dance of victory.
The images kept repeating themselves, except for a new one here and there. The most recent one was of their late night encounter, when Cas had visited because he was concerned about him. It didn't last long. The only thing he saw was a pair of eyes in the darkness. They opened and two green eyes were staring at him, irises wide for the lack of light in the room. Then the image was gone as suddenly as it had appeared in his mind.
“Hello Dean.” Dean jerked at the sudden sound behind him. He knew exactly to whom the voice belonged. Before turning around he took a deep breath to steady his thoughts, and when he did turn he was shocked at how close Cas stood to him. “Um, Cas? Personal space?” Dean only breathed the words, afraid that talking too loudly would make him disappear. “Certainly.” Cas took a step back, giving Dean room to breathe freely. Looking at Cas Dean noticed that his lips were somehow fuller, redder than usual. He ended up staring at them a little longer than necessary, so he didn't miss the tiny shiver that caught Cas' lips. Dean quickly looked away, he felt like his knees were about to give in. Had Cas noticed? He was suddenly very self-conscious, so his hand found it's way to his hair, tousling it and causing it to stand at funny angles. “Here, let me fix this.” Before Dean knew it, Cas was moulding it into it's usual style. When Cas' hand accidentally touched Dean's forehead it felt like an electric current was running through him, doubling it's intensity on the way back. Dean swore that for a second he didn't see Cas' face but his own in front of him, eyes wide, mouth hanging open slightly and his freckled cheeks flushed a little. The vision was gone as soon as it showed. Dean was startled. “Dean there is something I need to tell you.” “I'm all ears” Dean said grinning, and accidentally purposely brushed his little finger against Cas' hand. The current was there again, doubling on it's way back. And for a second he saw his own face before his eyes. “The blood we've been injecting you, it was my blood.” Dean smiled mischievously. “Cas, I already knew that. I did my own research.” “But did you know that there was.. some grace left in it?” It took Dean a moment to digest that information. Of course he had thought about the possibility before, but the only possible consequence of that would be... it would be that Dean wasn't only connected to Cas' memories, but also to his emotions. Reassured in his actions, Dean took a step forward. Their bodies were almost touching. He raised a hand and cupped Cas' face, forcing him gently to look up into his eyes. “Cas, you're in my veins.” Then he leaned forward, until their lips almost touched. Dean felt Cas' breath on his skin, he could almost taste him. Deep inside of him Dean felt something burning like hot coals. After looking up one last time to check if Cas really was okay with this, he was suddenly surrounded by an ocean of blue, of warmth, of love. Then they simultaneously closed their eyes, and their lips met. Dean's whole body was on fire, and so was Cas'. He had waited so long to do this, spending lonely nights longing for the man he loved, who was now in his arms, kissing him back gently. Dean carefully parted his lips and when Cas' tongue brushed over the sensitive skin he could feel something divine shifting and moving inside of him, banishing all the traces of his demonic self from his body.