The vampires appear out of nowhere and Sam and Dean have not come prepared to take on what seems like the entire nest.
"Sam! Watch your back!" Dean yells out to his brother as he takes off one vampire's head. Sam turns at the last second, his machete catching the monster at the neck and cleanly severing the head from its shoulders. Dean smiles to himself, grateful that he warned Sam in time, but fails to see the other vampire coming at his back. Neither of them can imagine what was coming next.
A large black haired vampire takes Dean down from behind, biting deep into his neck, and at the same time, the creature forces his shredded wrist into Dean's mouth. The blood flowing freely from the wound, Dean can't fight against the blood going down his throat. He swallows deeply, knowing that he is doomed.
Sam appears behind the vampire, one fast movement and the head goes rolling across the ground, but he knows he was too late, and as he looks down at Dean, and at the blood smeared across his face, he eyes fill with tears, and his mind races with ways to save Dean from his fate.
Driving back to the motel, they're both silent in the car. The fighting doesn't start until their motel room door closes behind them.
"NO Sam. I already know what you're trying to do. I'm a monster!" Dean screams at his brother, turning his back on him.
"Dean, we can find a way to help you. There has to be a cure." Sam begs, taking a step towards Dean.
Quickly turning, Dean looks his brother in the eye. "Sam, I can already feel the change, feel the need. I have to get away from you before I do something I know I'll regret later. Just go on with your life and forget about me." With those parting words, Dean is out the door, moving faster than Sam's eyes can follow. The keys to the Impala left on the motel table.