Dean somehow knew the look before it happened, and he was already moving when the light hit. "Fuck. fuckfuckfuckfuckfuck." He moved again once he could somewhat see, and was there to give the poor human Jimmy support.
"Fuck, man, I didn't think he'd actually do it." Dean had expected Cas to disappear or get angry, but just leave - as in leave the body behind so that he couldn't talk communicate anymore? It...it felt like he'd been abandoned, and he probably deserved it.
"Com'on, sit down." Dean pulled the chair out while offering Jimmy support. "There's a beer on the table if you want it."