"It's not..." Dean shook his head. But really it was, wasn't it? he glanced at Cas, looking for back up. "We're worried about you, Jo." He kept hold of her hand, shifting his grip so she couldn't pull away. He wouldn't forcibly hold her there, but he wanted her to know he wasn't just going to let go.
Hadn't she seen how the drugs affected Cas? Didn't she remember how it affected her to see Cas like that? Never mind how it affected him. And now to have to watch her doing the same thing, more or less. He and Cas had reached an understanding about his restlessness, his threats (both vocal and inferred) about leaving if things got bad, or didn't change, or didn't go the way Dean wanted. He had no such understanding with Jo, and he found himself wondering just where that line was drawn, with her drinking and using drugs to self medicate.