It occurred to him that one day, his brother was going to die.

Sam's eyes flew open the moment the thought crossed his mind. He sat up, heart pounding against his ribs, the breath he had seconds before gone. One day Dean was going to die. No matter how many demons they killed, how many people they saved, he would die. His heart raced faster and his body moved on its own, jumping out of bed and not wasting anytime to begin pacing around the room. He ran fingers through his hair, begging himself to think of something – anything- that would calm him down. Nothing came.

Someday, Sam could very well be alone.

What will do him in? A voice asked. A demon? Vampire? Car crash? Old age? The last one would at least ensure the elder Winchester a long, fairly happy life. That was some sort of comfort, right? At that time, not at all. Death was death in Sam's head and his brother's had sent him into a complete panic.

Panic…

"A panic attack," he breathed. That's all this was. He just needed to breathe. He sat down on his bed, closing his eyes, willing the dark thoughts away. He thought of their wild goose chase for Abaddon.

Mark of Cain. The voice was back. Maybe that'll kill him.

He thought of riding down the long expanse of highway, Dean driving and making conversation, his voice barely louder than the music.

Car crash. Suddenly a truck collided with the Impala and Sam saw his brother's head hit the glass, blood splattering against the door as his mangled body twisted with the movements-

"Stop!" he hissed, grabbing his head. "Stop." It was childish to argue with himself, but at this point, there was nothing else to do. Cas was still on the road on his business and Sam couldn't bring himself to give the angel a call. Besides, his only comfort would be Dean's soul in Heaven. Even that, the image of Dean, happy and laughing, surrounded by their loved ones, wasn't enough. It was selfish, sure, but Sam didn't want Dean anywhere if it wasn't with him. They weren't supposed to be apart. It didn't matter how many fights were started or how many names, threats, and hollow declarations were thrown around. The brothers would always be together. That's just the way it was supposed to go.

He considered going to talk to Dean about the whole issue, but he couldn't bring himself to leave the room. No matter how many times Dean claimed he was okay, Sam knew better and he knew that his brother was getting zero sleep. Just the thought of him waking his brother up over something as trivial and inevitable as death shot a dose of guilt through him. He was no longer a gangly ten year old who cried to his brother every time lightning broke the night sky. This was his problem in his head.

"He's going to die," Sam muttered. "He's going to die. He's gonna die and there's nothing you can do about it."

"Who's gonna die?"

Sam jumped, facing Dean. Too caught up in his own thoughts and fears, he missed the sound of his door swinging open. His brother was leaning against the frame, arms crossed as he studied his brother. The concern on his face only served to enhance the bags under his eyes and the lines between his brows.

Has he always had those? The thought of aging sent another wave of panic through Sam's gut, and out of instinct, he tensed. That didn't go unnoticed.

"Sam, what's wrong?" Dean straightened up a little, just now noticing how wide Sam's eyes were as they flitted around the room, looking at everything in the room but him.

The younger Winchester took a breath, forcing himself to remain steady. "Nothing, Dean," he muttered. "It's nothing."

"Bullshit. Something's up." Dean walked further into the room, his annoyance quickly melting once he realized how scared Sam seemed. "Sammy, tell me what's wrong."

"It's nothing," Sam repeated, but once he opened his mouth, the floodgates opened. "It's nothing. It's stupid. I know you're going to die one day. We're all gonna. Hell, we've died before, haven't we? I mean, technically, yeah. I shouldn't be panicking over something that everyone has to go through at one point or another. I mean, I'm not the only one with a brother or someone –"

Dean put his hands up. "Woah, woah. Slow down. You're not making any damn sense." When he was sure that his brother was finished, he added, "Now what's this about me dying?"

"You're going to die one day. Even if we survive all this, eventually, you're going to die."

If the situation had seemed any less serious, Dean would've laughed. "Well, yeah, I am. So are you. So will everybody."

"I know that!" Sam snapped and then paused, kneading his hands together and looking more like a child than he had in years. "But Dean, you're going to die."

And just like that, Dean understood. He crossed the remaining distance between the two brothers and sat on the bed beside Sam. The two of them sat there in the silence, staring at their feet as Dean tried to find something to say and Sam wished he had never said anything at all. The air was just as heavy as it had been in the past few months, but ironically, they had never been closer. Dean felt terrible for it, but a wave of relief had passed through him when he realized that Sam truly and honestly did care whether or not he died. Him trying to stop it was still up to debate, but he cared. After a few more moments, he looked at Sam, who still had yet to raise his head.

"So, yeah," Dean started. "I'm gonna die. Might be tomorrow, might be fifty years from now. But it'll happen."

"You're not helping."

"Now, now, hear me out. I'm just getting started." He clapped a hand on Sam's shoulder. "Sure, I'm going to die, but do you really think that you're going to be alone? We've got an angel buddy, Sam. He can… I'll just use him as a carrier pigeon or something." That got a small smile out of his little brother. "I'm not going to just run off to the afterlife and forget about you. And you're real naïve if you think that me dying is going to make me leave you alone."

"I know, I just…" Sam looked up. "We've been on the road together for almost ten years, Dean. Ten years."

"And we'll be on the road together for a hell of a lot longer. Listen." Sam finally looked at him. "I can't comfort you by telling you that I won't ever die or that we'll die together or anything of that. Hell, I don't even know if what I'm telling you is going to do you any good. But what I can tell you is even if I do die first, we'll still be in touch. And I'll be waiting for you get your lazy ass up there." Dean cocked an eyebrow. "But if I do die first, don't you rush anything, you hear?"

Sam smiled and nodded. "Yeah. I hear." His fears were still ever present, but just addressing them had made his panic subside. Relaxing his shoulders, he put his hand on Dean's. "Thanks, Dean."

"For what? I don't think I was any help."

"Believe it or not, talking about your feelings helps just about anything." Without meaning to, Sam had open fresher wounds. Instead of calling him out, though, Dean just nodded and stood up, removing his hand from Sam.

"Yeah," he said, "well, just let me know if you gotta talk some more."

Sam nodded. "Thanks again, Dean."

"Get some rest, brother." Dean walked out, closing the door behind him. He let his mind take over as he made his way down the hallway. So he was going to die one day. So would Sam. He realized as he entered his room that there was a chance that Sam could very well be the brother who died first. But try as he might, Dean couldn't bring himself to fear that anymore. He dropped down onto his bed.

Regardless of who died first, the second Sam could get away from Dean, the better chance he had at happiness.