1. John Winchester
For the bruises and the hungry nights counting pennies and the way Sam stops asking when John is coming back. For the way home is a gun in Dean's hand and blood on his knuckles.
It's easy, forgiving John; it's as instinctual as making sure Sammy eats first.
2. Mary Winchester
For dying and for coming back. For dying again.
For being human.
3. Sam Winchester
For betrayal after betrayal after betrayal. For Ruby, for sacrificing himself and expecting Dean to live with it, for not looking for Dean- or maybe for not needing to. Because Dean can honest to God hate Sam, sometimes, but he never learns how to stop loving him enough to forgive him for anything.
4. Jack
For killing Mary. For existing at all. For being the son Dean never always wanted and not the monster he should have been.
5. Cas
For saving him from Hell, from the Devil, from God, from himself. For leaving him, every goddamn time Cas walks away intending to never come back.
Dean's never been sure which is worse, just that it's the hardest thing he's ever done to forgive Cas for the way he never feels whole again after the one thing Dean's ever found worthy of praying to saves him and leaves him one last time.