Sam cried. Face buried in his hands, lungs burning from lack of oxygen intake, entire body shaking so hard he was surprised he was still sitting up, he let out one guttural, gut-wrenching sob after another and wondered if it would ever stop.
When Sam was seven, he'd wrecked his bike and scraped all the skin off his knee. That had hurt pretty badly. But when Dean had patched him up with a bandage and a kiss to the forehead, the tears had dried, and Sam had realized that it wasn't the end of the world.
A while later, after he'd hit puberty, Sam got his first girlfriend. Who then proceeded to cheat on him and dump him for a douchebag whose name she hadn't even bothered mentioning after they'd been together nearly a year. "Girls, man," Dean had said, lying in Sam's bed beside him and gently playing with his hair. "Almost never worth more attention that one night. She didn't deserve you, anyway, Sammy." As long as Dean believed Sam had been too good for her, then it had to have been the truth, right? That was the first night since they'd broken up that Sam went to bed without crying himself to sleep.
Just before Sam graduated high school, a routine father-son fight had finally gotten so out of hand that John had hit him. Sam wasn't sure if the moisture rolling down his cheeks was from the shock, the pain, or the idea that his own father could do something like that to him. But when Dean had pushed open the door nearly an hour after Sam had gone into his bedroom and Sam caught a glimpse of a passed out John with a bloody nose lying on the floor outside, Dean had simply whispered, "It's okay, baby boy. It'll never happen again. I promise. Everything's taken care of." And, of course, if Dean said it, Sam believed it. So, really, there was no need to cry anymore.
Now, though... Now there was no one there to make the tears stop coming. And that was precisely why Sam was crying. There was no Dean. Dean was dead. Gone. And he wasn't coming back. Ever. So Sam didn't even attempt to control himself. He just cried and cried and cried.