Dean has to burn Kevin by himself.
Charlie is in Oz. Cas has his Grace back, and no longer has to have anything to do with him. Sam is god knows where, with a rogue angel riding him, and he's not even sure if his brother is still alive in there or if he has been obliterated. He has no one left, and nowhere to go.
Dean can't even look at the body, still bleeding and smoking on the floor.
He takes the axe and walks into the forest, finding a suitable tree and starts chopping. It's still light when he starts, and he has to stop numerous times to angrily wipe the wetness spreading across his cheeks. He has to drag the tree back through the brush, and finally stops to chop off all the small branches that were catching on the underbrush.
It takes the night to cut the tree to the right lengths of wood, and when Dean is done he piles it up behind the bunker, and soaks the pile in lighter fluid. The wood soaks it up slowly, the green wood not taking the fluid slower than dry wood would have.
Dean swears silently to himself when he realises that there is a pile of wood that he could have used behind the bunker, the wood dry and susceptible to fire. There's still tears gathering in the corners of his eyes, and he hates himself, hate the world, because Kevin was family dammit and why did this happen?
He piles the wood up and makes sure there was a way to get the body up onto the pyre.
He wraps Kevin's body in a bed sheet, hiding the burnt out eyes that still seemed to stare at him even when he covers them over with the white fabric.
He shoves the body over his shoulder, and walks up the bunker stairs, their last conversation he had had with Kevin running through his head. Stupid stupid he was so stupid.
He flicks out his lighter, and closes his eyes before dropping it on the pyre.
The wood goes up with a whoosh that Dean doesn't need to look at to feel and the heat makes him need to step back. He watches the fire burn, and the vibrant light of the fire blocks out the dawn until Dean looks up and realises that there are no clouds whatsoever. The sky is red, echoing the blood that is still staining the floor of the bunker and the crimson tears that Kevin had shed, the last statement that he will ever make.
Dean stands there until he can no longer see the white gleam of bones and ashes are the only thing left.