Even with the little smile, Liv knew better than to think he'd calmed to a safe point. He was maintaining, but if he was left to marinade in whatever it was that drove him to this edge, he'd go over it and take Sam with him- possibly more people, if they got in his way.
Liv would definitely be in his way, and she knew she could do her fair share of damage if she needed to, but she was all about avoiding the whole mess. Because even if Dean managed to satisfy his timebomb anger without taking out half the town, he'd be without a brother, and he would never forgive himself. She knew him well enough to know that without a single doubt.
He squeezed her arm, and she squeezed back- all the way through Granny's front door, where she caught the first employee's eye she could and pointed at the back booth. "One whole cherry pie, please. Two forks and a can of whip cream. And a pot of coffee." That wasn't a reassuring squeeze he'd given her- it was a desperate cry for help from a man who would never say the words. She even sat next to him in the booth instead of opposite of him. The empty seat just held her dirty labcoat.
"I'm just gonna go'head and tell you right now," she said almost right into his shoulder as he settled- keeping her voice to just them. "I'm not going anywhere, and I'm not letting you out. Not 'til we've got a recovery plan and we're both laughing at your bad jokes. That's not a threat or a demand, okay?" She locked in on his eyes- her's were back to normal, and full of raw honesty and determination. "That's a promise."