I'm a little late to the Supernatural game, I've just gotten done watching the series on Netflix over the past 4-5 months so this story takes place a little in the series' past, season 11 episode 13 "Love Hurts." Like many I read a bit too far into the brothers' relationship, but the inspiration for this story came from how close they are. If you don't like Wincest don't read and obviously I own nothing from Supernatural, just this idea.
Sam felt a little spark of jealousy that he immediately stamped down. Dean only kissed Melissa on the off chance it would force the "return to love" curse away from her and onto him. Not to mention Dean was never his to begin with. No matter how Sam felt, the only claim he had to Dean was as a brother, and certainly had no right to get angry over any person Dean chose to kiss.
As it was the kiss seemed to work. The brothers took the brief reprieve and pulled Melissa from the room. They ran from the motel room without noticing the shadow of the shapeshifter changing. It got a bit shorter, the shoulders broadening, and the stance stronger.
In the car Sam feels his frustration building. The kiss itself was bad enough but now Dean was marked for death, again. Did his brother really have such a hard on to die that he had to intentionally get a curse put on him? He began to argue about it with his brother who of course stood his ground as if he'd done nothing wrong. And in Dean's mind he hadn't. Dean had a bit of a hero complex in general, though it was of course worst when it came to Sam. Eventually the two stopped arguing when Sam realized there was nothing he could do about the situation other than kill the shifter. Or kiss Dean… NO! Sam stopped that thought before it could fully form in his head. If he'd let it develop he would have sat there fantasizing about kissing his brother like he had been since he was 14.
After some discussion Sam and Dean figured out from Melissa that the hairdresser she'd gotten the spell from worked her witchcraft out of the basement of her salon. After arming Melissa and telling her to wait in the car the two crept slowly into the salon. The business was empty but that was no indication of what might be in store in the basement and the brothers walked cautiously down the stairs. It was a fairly derelict basement, completely unfinished. However they did find the witch's grimoire, which spoke of her spells. They found the curse in question and realized that it harnessed the power of a creature called a qareem to punish the victims the curse was directed towards. The qareem took on the appearance of the targeted victim's deepest and darkest desires before it killed them. Sam was instantly grateful he hadn't kissed Melissa; he didn't think he could stand seeing the disgust in Dean's eyes when he realized he was his brother's deepest, darkest desire.
They finally figured out that the way to kill the monster was to stab its heart. The only problem was the qareem's heart didn't reside in its body, the witch in question held it. So Sam and Dean played rock paper scissors to see who would get to go upstairs and look. For once Dean won, but he was so excited that he didn't even complain that Sam himself went upstairs to look for the heart while he looked in the basement. After a bit of searching Sam found an old looking box that's locked, he was sure that the heart had to be in there so he began to pick the lock. Before he could get the box open he felt his body lock up.
Looking around he noticed the hairdresser standing there just as he heard bumps and bangs from the basement. Sam struggled as hard as he could, knowing he wouldn't be able to move while the witch had him under her spell, desperate to save Dean and stab the heart. Suddenly Melissa burst into the salon and begged the witch to stop, to break the curse and stop hurting the hunters. The witch flung Sam away towards the door to the basement and he tumbled down the stairs. It took a minute for his head to stop spinning but when it did he saw Dean fighting Sam. Sam thought he must have hit his head harder than he thought. Then he realized that Dean was fighting the qareem, the qareem that took the shape of Dean's deepest and darkest desire, the qareem that looked like Sam.
Before he could put too much thought into it Sam ran back upstairs. He could hear Melissa choking and knew the witch was attacking her. By the door to the basement he spotted his gun, the gun with special witch killing bullets. He grabbed the gun before the witch could spot him and shot her. Immediately Melissa began to gasp for breath and Sam ran for the box with the heart as he heard Dean grunting below, knowing he was losing. He picked the lock on the box and grabbed a pair of scissors before stabbing the heart. Sam heard a loud scream from below then silence. He checked Melissa to make sure she was fine and then ran downstairs to check on Dean. Dean acted nonchalant as ever, pretending the encounter was no big deal, though there were holes punched into multiple surfaces in the basement and Dean couldn't look directly at Sam.
Back at the motel Sam and Dean began to pack up their things quietly until Sam voiced the opinion that they could both use another night of rest before hitting the road. His body was sore from the grip of the witch's spell and he was sure Dean was just as sore from his fight with the qareem. Plus, though he would never voice it out loud, Sam was dying to talk to Dean about what he'd seen. Dean left to head to the manager's office to rent the room for one more night and get some food and beer, and Sam sat on the bed and thought about how to best bring up the subject of the form of Dean's qareem.
Before Sam could marshal his thoughts into a proper order Dean was back with a six-pack of beer and some food for the two to share. Sam felt anxious, the beer would have the ability to loosen Dean's lips a little, but it could also start a real argument if Dean became defensive, which was usually his go to attitude when it came to feelings. Sam decided to start the discussion off light, almost jokingly, after they'd both had two beers, by asking which Daisy Duke the qareem had taken.
He expected Dean to laugh, but instead he got serious. "It was… Amara. The qareem became Amara. I'm not sure what it is about her Sammy, whether it's an aftereffect from the Mark or something else, but I'm drawn to her. And Sammy, I want her dead, I want to kill her, but I can't kill her." He turned to face Sam and Sam could see the look in his eye, embarrassment, shame, but also something deeper, guarded, something he was trying to hide from Sam.
Looking back Sam could never quite say why this set him off. If he had been honest the qareem becoming Amara would have surprised him less than it had when he'd seen himself attacking his brother. But for whatever reason, he began to feel hurt. His brother was lying through his teeth, looking him dead in the eye, and saying his deepest desire was Amara rather than Sam. Sam had finally seen with his own eyes that maybe he wasn't a freak for loving his brother. Maybe, though it was wrong, that he wasn't alone, that his love wasn't completely unique. Instead of admitting that to Sam, Dean wanted to lie, and that hurt Sam, and made him angry.
"Fuck you man!" Sam shouted. Dean's eyebrows shot up as his eyes widened and he jumped in surprise. "You're going to sit there and try to sell me this bullshit about your qareem becoming Amara?! You know, if I hadn't seen it with my own two eyes, I'd have believed that. I could logically understand why you two would have a connection. But I did see it with my own two eyes Dean, I saw you fighting me. ME!" Sam stood up and began to pace back and forth as Dean sat there stunned, his mouth hanging open in shock, unable to say a word.
"Am I really that undesirable to you? Am I truly so loathsome that you'd rather lie and say the Darkness, the thing that wants to destroy the world, is so much better than me? That she's your deepest desire? I know I've messed up quite a few times in my life. I know I'm a guy, your brother no less, but I thought I was at least better than the Darkness. And then to have you sit here and tell me, knowing that you saw me, that you saw her. To hear you say that she's your deepest desire… Dean I didn't know you hated me so much, that you were so disgusted by me. I thought, for the first time ever, that maybe you loved me that way too." At those words Dean turned to Sam, disbelief and the hint of hope on his face. But Sam missed the look, sometime during his tirade he'd begun to cry and his vision was blurred. He sat on the bed, turned away from Dean and started to cry harder, unable to continue.
Dean's heart broke as he saw Sam start to cry, as his brother's words finally broke through the stupor that had settled in his mind when he learned that Sam had seen his qareem, his deepest desire he'd hoped Sam would never find out. Because how could Sam ever love him, ever look at him or even be around him, if he knew what Dean felt? Dean had been in love with his little brother since the kid was 15 years old. It had been wrong, for so many reasons. He'd been so young, he'd been a guy, and he'd been his brother. Any and all of the reasons had been so horrible, he'd hated himself for so many years because of it. Dean had turned to drinking, to whoring himself out to loose women at dive bars, all to escape his true feelings.
And suddenly, Dean realized, he'd have been better off risking having his brother hate him, be disgusted with him, rather then see how heartbroken he'd just made Sam. Sam was his life, his whole world, since he'd been born. He'd raised Sam, taken care of him when John was out hunting, made sure he was fed and bathed, slept and did his homework. And even when they were both older, he'd always looked out for him. Trained him to hunt, jumped in front of the monsters, even bore the brunt of John's anger when he could. Sam was his life, yet he'd never realized that he was just as much Sam's as Sam was his. He never saw how his brother felt, he'd failed him, and now he'd just made Sam think he was disgusted with him. He had to make it right.
Dean moved slowly over to stand in front of Sam, and then he kneeled on the floor in front of him and took his baby brother's big hands. "Sammy… I'm so sorry. I never want you to think I'm disgusted with you, not ever. You're the best thing in my life Sammy. You're so positive, so steadfast and calm, so thoughtful and sweet. You're such a good person, even when you make bad choices, it's always with the best intentions. I've never for one second thought less than the world of you. Even when you piss me off, even when we fight, you're still the best person I know." Sam got quieter and looked at Dean, he seemed confused but he was blushing. Dean bit his lip at how adorable he looked and continued. "Sammy the reason I said it was Amara was to protect me, not to hurt you. I've been in love with you for years, but it was so wrong for so many reasons. I figured you'd be disgusted, that you'd hate me. I never for one second thought you'd feel the same or I would have done something I apparently should have done years ago."
Sam's eyes were dry now, and wide with shock. Even after seeing the qareem he'd never imagined that Dean would admit how he felt, that he'd tell Sam. And now he was leaning forward, his lips so close to Sam's while their eyes locked on each other. Dean stopped a fraction of an inch away and his eyes held a question, asking Sam for permission. "Dean… please." Sam said before Dean sealed his lips shut with a kiss. Sam knew in that moment that even though it was wrong, even though society and the laws of nature would say they should never be together, that this was right. He felt complete, Dean was his other half and he was Dean's.
Dean pulled away from the kiss with a little smile and said, "You, Sam Winchester, are my deepest desire. You have been for years and you will be always. I need you in my life more than anyone or anything else. And if you'll have me, I'll always be yours."
Sam smiled and simply said, "I love you," to which Dean smirked and said, "I know." Sam laughed briefly at the stupid Star Wars reference his brother would make, and he called Sam the nerd, before pulling his brother's lips back to his, where they would hopefully stay for the majority of the night.