It takes Dean and Cas six months to make it to the outskirts of the settlements. The monsters look closer to human here, but are no less deadly, and the building is packed with them.
After six months, Dean is used to fighting. It lets him escape, to not think about his situation, just act. And there's a satisfaction that comes with slashing through the hoards of creatures, with knowing that Cas has his back, and working seamlessly as a team. These days, Dean finishes a fight with a smile on his face.
They clear out the building, honeycombed with apartments (and Dean thanks whoever's listening for the fact that it's been months since Cas last rambled on about bees), and choose the least decrepit one to spend the night.
While Cas is painting the crumbling walls with wards, Dean paces the room. There's a narrow, dusty palate for sleeping, a rickety table, and a single chair with a broken leg, but otherwise the room is bare. He looks out the window at the decaying settlement, buildings packed close together, vaguely humanoid creatures staring out of the shadows with glowing eyes, and finds that he's looking forward to tomorrow.
He's looking forward to the next fight, the next burst of adrenaline coursing through his body. There's a simplicity to life here - the goal is survival and that's it - that Dean doesn't hate. And with each passing month, Dean has had to admit to a greater possibility that they'll never make it out. And the thought bothers Dean, it does - because Sammy's waiting for him, he has to get back to his brother - but it also kind of doesn't.
Purgatory is made of decay and corruption, the building he's in is falling apart around him, but Dean feels more whole, more alive, than he has in years.
Cas is finished with the wards and leans, weary, against the wall. Dean smiles at him, because that's the other thing he enjoys about fighting: that after six months of fighting side-by-side every day, he and Cas fit. They can sense each other's movements, predict what the other is going to do, and what they're going to need. It's that sense of connection that keeps Dean going, that makes each battle feel like an awesome feat, instead of a grim bid for survival.
Cas smiles back, tired but fond.
It suddenly seems to Dean like the most logical thing he can do is go to Castiel and kiss him. He doesn't examine the thought, because this is Purgatory, there's no one to judge him, and he might not even make it out alive, so what does it matter? He does it.
Cas kisses him back, and this too fits. Dean feels whole, and alive.
Castiel ends each day a little more tired than the day before. Then Dean kisses him, and the touch of Dean's lips does something to him, makes him feel things he didn't know he could, and he doesn't know what it means, but it must mean something. The touch of Dean's lips breaks him apart, but he doesn't care. Purgatory is slowly killing Castiel, but he doesn't care.