His eyebrow quirks a hint; that's all there is when Jo...singles him out. Geralt has the sense her reaction bothers Dean more than it does him, which is not an understanding he knows what to do with nor one he wishes to examine right at this moment. He's clearly stepped into a field of daggers here. The truth is, he isn't keen on standing about to see how it unfolds. This isn't his business, it isn't his conflict. He is an easy excuse for whatever turmoil Jo has towards the situation—seeing Dean again. This tavern.

Still. Dean says, If I stay, he stays, and he leaves behind any thoughts of walking away.

Through the exchange, Geralt is silent. He doesn't care about defending himself; he can't give a fuck what she thinks. She can believe what she wants or call him what she wants; he's long used to it. But he does care about Dean being caught in the middle of this nonsense because she's too entangled in her own bullshit.

He lets his gaze linger on Dean for a moment. "He looked after someone important to me."

As in: yes. The trust goes both ways. It's meant for Dean as much as it is for her. Maybe more so.