I do really wonder what the previous understanding about the joint account was. If there was a standing agreement that they could both use that money under their best judgement and LW is rethinking it when it's Husband loaning to parents rather than LW paying for car repairs, that's different than if he's violating an understanding that they would consult each other. (It also matters if he did it spur of the moment and then told her, or if he kept it secret; and what percent of their savings it was; and so on.)

It also doesn't say if there are any accounts other than the joint one - there may not be - or even, now that I re-read, if the $11,000 even came out of the joint account! This could be "He's wiped out his own savings supporting his parents so now I don't trust him with shared money either." If Husband is in the US he's on SSDI not SSI or they couldn't even have 11,000 in a joint account, so his disability may be enough to have some of his own savings.