Wow. This was just so beautifully written. I love how Sam thought he had all these secrets he'd kept hidden from Dean, but in reality he didn't. And I just love that Dean knew the secrets, but never let Sam know that he knew.

And then the last line. Dean knowing that Sam is going to kill him, to save him and his soul from Hell, and understanding why. And then that last line...the two bullets. It brought tears to my eyes. Poor boys.