Either this is a significant personality change that would indicate an illness requiring treatment, or this is who he’s secretly always been in which case you’re really not losing anything but your illusions and if this is the last time you see him then you’re not really losing anything important.
If it’s the former it may help you to feel better by trying to get him some help, even if you fail then at least you tried. If it’s the latter then it’s just best to cut your losses as soon as possible and move on.