Dean historically doesn't react fantastically to news about his baby brother. Bad news about his baby brother, he reacts to even less well. So it's really no surprise, in his mind, when Cas says all of that and Dean jerks at his jacket, shaking him, voice low and rough and uneven.

"He's-- are you shitting me right now? Cas, Cas, everything I did- I promised him I wouldn't let anything happen to him! I let him do those trials and I--"

Failed him. Dean falls silent, biting off whatever he was going to say, and jerks back, breathing shaky and uneven. Behind him he hears the crunch of grass as Tessa steps forward, and presses her hands to his shoulders, and he sinks into that a moment, staring at the ground.

"Why didn't you stop him?"