Dean didn't let himself get emotional very often. In his line of work, it wasn't exactly an option. And even though Madison was a great girl who didn't deserve any of this, he normally would have forced any regret or sadness out of his mind. But this was different. Sammy was crying.
Whenever Sam cried, something inside Dean broke. This was one of those times. He had seen the pain clearly in Sam's eyes, and knowing that he couldn't save his brother from this almost killed him.
"Sam..." he said, almost whispering. He knew what he needed to say, what he needed to do, but he had to see Sam's face first. Slowly, Sam turned to face him, tears flowing openly down his face. "I'm sorry," Dean continued, knowing that it meant nothing, but feeling compelled to say it nonetheless.
"No, you're right," Sam choked out, clearly trying to maintain some level of calm. "She's right..."
Sam's tear-stained, miserable face broke Dean's heart, his resolve almost shattering. But he knew what had to happen, despite how hard it was. Maintaining a stone face as best he could, he said, "Sammy, I got this one, I'll do it."
"She asked me to," Sam said immediately.
"You don't have to," Dean countered.
"Yes, I do." Fresh tears spilled down Sam's face, and he dropped his gaze to the floor. Soon he looked back up, meeting Dean's eyes with as much determination as he could manage. He held out his hand, saying, "Please."
Dean didn't want Sam to do this, especially not while he was there to take this weight off his brother's shoulders. That was his job after all. But something in Sam's eyes convinced him, and he reluctantly handed over the gun.
"Just wait here," Sam said before slowly turning and heading out of the kitchen. Dean desperately wanted to stop him, snatch the gun back from him, protect him from this. But he knew he couldn't. No matter how much it hurt, this was Sam's choice.
He watched as Sam paused in the doorway, allowing himself one last tear-filled look at Dean. For a second, he almost looked like he was about to change his mind. Then he turned away and steeled himself, taking a deep breath before walking into the room where Madison was waiting.
Even alone, Dean kept up his mask to disguise the pain. He couldn't let Sam come back and see him weak. He had to be the strong one, like always. He had to be strong for Sammy. But despite all his best efforts, a single tear slipped out against his will.
He flinched when he heard the gunshot. But as hard as it was, no more tears fell. He would be strong. He would protect Sam.
That was his job.