Looking back these past few years, Sam Winchester had come to realize that no matter what you do, you can never run away from destiny. His father knew it, the Yellow-eyed demon knew it, and now he's finally accepting that fact too. No matter what he does, no matter how hard he tries to convince himself and others otherwise, he can't change who he is.
He is meant to be Lucifer's vessel. He is meant to aid the fallen angel in destroying the world and change it forever. That is his role in this life, his purpose of living. As hard and bitter as it is to swallow, Sam can't deny what has always been meant for him.
This is his destiny.
After everything he fought for, everything his brother sacrificed to save him, only to come find themselves facing this grim fate. Ironically, the one that has always kept him from harm is the one that is supposed to stop him, no matter what the cost.
It seems almost poetic, in a way. Two brothers facing off against one another, one dark, one light. One brother ends the world and the other saves it.
Lucifer and Michael.
Sam and Dean.
Sometimes he'd lay awake at night, just staring up at the ceiling, Dean deep asleep in the bed next to him. His mind would wander and he'd think of the different ways Lucifer could come up with to finally push Sam off the edge, to finally make him say yes. He'd imagine Dean bleeding on the floor, body broken in states he knows can't be fixed. He'd see Bobby screaming as hell hounds tore him apart. He'd hear Lucifer consoling him, offering him a way out, offering to take the pain away from him.
And then Sam would wonder if that's enough to make him say yes.
Sometimes his imagination would take the form of Dean facing him, standing tall and proud, eyes burning with hate and disgust as he aimed the Colt straight at Sam's head. Bobby and Castiel would stand behind him, ready at any moment to defend their savior.
"You worthless piece of shit," he'd hear Dean saying. "After everything I gave up for you, everything I sacrificed, this is how you repay me? You're freaking Lucifer, Sam! You know," Dean would shake his head. "I never thought I would actually say this, but I wish you died in that fire with mom. Then none of this would have happened! Jo and Ellen would still be alive. Bobby would be able to walk. I wouldn't have gone to hell for you! ".
There a definite possibility Sam would say yes if that happens.
So that's how Sam spends his nights nowadays. Sure, maybe he doesn't have the healthiest train of thoughts and Dean would probably kick his ass if he ever finds out but seriously, who was he trying to kid?
He can't do this. He's not strong enough for this. How the hell, pun intended, was he, a disgraced hunter with an addiction for demon blood supposed to fight Lucifer, the Morning Star, a fallen angel? How long will he able to resist him?
He knows he can't give up, won't give up but he also knows that you rarely get what you want. He knows personally that life has a funny way of kicking your ass, chewing you in and then spitting you out.
He's trying to be strong, he really is. But sometimes it's so hard to not just crumble to the ground and cry. Sometimes it takes everything in him not to just give in to the darkness that he knows is just waiting to consume him.
Sam's trying so hard.
But despite his destiny, despite his powers, despite who he's meant to be, he's still only human, still flesh and blood.
And there's only so much that he can take.
One of these days he knows he's going to fall. One of these days he's going to break. One day his brother will finally realize that Sam isn't as strong as he wishes to be. One day, Dean will face him and find him unrecognizable.
Until then, Sam fights. Until then, Sam is left with the endless possibilities of what could be.
Until then, he waits.