A/N: Taken from Season 2, Episode 17 "Heart." I don't own any of the Supernatural material, I'm just part of a humble fandom.
Watching Sam take the gun and disappear into the other room where Madison waited, Dean gritted his teeth. There were very few things that broke the surface of his armor, but Sammy had always been one of them; and at that moment, seeing tears run down his brother's face, his hands shaking as he took the gun, Dean wanted more than anything to stop him–to save him. That's what he'd always been good at. From the time Sam was six months old, Dean had always been protecting him. Not just physically, either, but emotionally, spiritually–if he really thought that you could be saved in that matter. Dean was more rough around the edges than his brother. He could do what needed to be done, without having an internal emotional battle. He knew that he could always do what needed to be done in order save people; for the greater good (except when it came to Sammy, but that's a whole other realm in its own). Sam was too softhearted sometimes, too naive. He hadn't been as invested in "the life" as Dean and his father had been, that's how he managed to escape for a few years and live a normal college life; but, Sam got dragged back in–that's how it always is–you never really get out.
After their father revealed that Dean might have to kill Sam, after what the Yellow-Eyed Demon had done to him, for whatever purpose he might have, Dean just wanted to put Sam under a rock for ten or so years; shelter him like a suburban soccer mom, protect him from whatever disease was inside of him. Sam probably knew it, too. Dean hadn't ever said it, but it scared the hell of out him. He couldn't lose Sammy, if there was one thing tethering Dean to this world, it was him. The boys had grown up knowing two things: monsters are real and family is everything. Dean wouldn't ever leave his brother, while he could be a know-it-all, pain-in-the-ass...he loved him more than he loved himself.
Sammy was good, innocent. Dean thought that, if you could save a soul, then he'd do whatever he could to keep Sammy's as clean as one could, when living the life they did. Dean could do the things that Sam couldn't. He could mangle his soul, load himself up with guilt, and sacrifice the things he had to. He was strong enough. He could keep all that blood of Sam's hands, off his conscious. He could be the anchor, the rock, the big brother that his father had raised him to be. If Sammy was okay, well...then Dean would be too.
Dean released the ragged breath he had been holding and a single tear fell down his cheek.