[Sometimes, the most obvious answer is the most simple one. Here Vash is, casting suspicion and doubt over these people that Ain very clearly trusts...and the answer Eve gives as to why they won't double-cross them makes too much sense. They're all trying to hide. They don't want to be found. It's why so many other criminals likely find refuge here, at least to a certain extent.

And Vash feels an immediate wave of shame wash over him, as if his brother is watching him right now, pleased by his "progress". Since when did he become so...suspicious? So unwilling to accept, or trust? To have hope?

It's not him. It's not Vash. Maybe it's in part due to his worry for Ain...but whatever it is, he's humbled by a single sentence.

It would be betraying Ain's trust.]

...I understand. [He murmurs, brows upturned as he looks away now, glancing over at the aforementioned windows.] I'm sorry. I don't mean to doubt...any of you. I just want to make sure Ain...and all of you stay safe.