Dean had felt alone,, no matter what company he kept, ever since he'd lost Sam. Cas offered him the most comfort, but he tended to take his stress out on Cas. It was a intense relationship, but even Cas couldn't fill the void left by the loss of Sammy. All these years later Dean knew that was his biggest problem. He just couldn't get over the failure. If you can't save your brother, kill him. That's what Dad had said, and Dean had denied it, and Dean had failed them both.
Being this close to Jo brought it all back to the front again, because Jo had been part of that life. Jo had given her life for the fight. That meant he'd failed her too. Dean's entire life seemed to be a series of failures, each one more epic than the last.
"Good, good. You're on that task then. That's good." If nothing else, he hoped giving her a specific task would help her feel useful.