It was an affair, an infidelity. A complete betrayal of the trust he'd had in her, and he knew the trust Faith had had in Sam. The fact it wasn't sexual was almost irrelevant. Castiel's head dropped down, as he tried to calm down.
"How could he ever have made the world better? He'd have turned it into his hell, his kingdom. And in helping him, you twisted Sam's humanity, maybe irreversibly. What you've done to him is sick, do you even see that? It's evil and wrong. Nothing special about it."
He looked up sharply, eyes flashing with anger.
"How quickly you forget. I defied God for you, my Father, my creator. And my faith, my faith is about love and creation. Yours is about hate and destruction, that's the difference."