I do not own supernatural or those gorgeous boys.
(What I think Dean might have been thinking as Sam shot Madison in the episode 2.17 Heart)
Dean would do anything to change places with Sam right now. Anything to take away his little brothers tears, his pain. If only he'd won their game of rock, paper, scissors. If he had won then he would have stayed behind to watch the girl, it would be him in this position and not Sammy. It would be him that had to put a silver bullet through her heart. Dean had tried, he told Sam he had this one, that he would do it for him but Madison had asked Sam to do it and Sam wanted too even though it was ripping him apart. Dean knew Sam was doing it because it was the only thing he could do for her. As the gun shot rang out through the apartment it tore at Dean like it never had before, made he physically flinch. Dean was used to guns, used to their sound, that's not what made him flinch. As the silver bullet had pieced Madison's heart Dean felt Sam's heart break and his own a long with it. A single tear slid down his cheek. He'd tried so hard to keep Sammy safe. Safe from harm, safe from pain. He'd failed again. But he would never stop trying.