Grindelwald had access to the Graves family fortune for months. After his arrest and Percival's subsequent recovery Graves discovers that he is utterly broke. And no longer fit to be an auror. (injury, ptsd, compromised, what have you.)

Graves ends up on the streets until someone finds this shell of a man and saves him. He gets a meal from a soup kitchen Credence is working at. Grindelwald won't let his talent be wasted. Whoever, whatever.

+His pride makes him do stupid things.
++ he does whatever he has to to get by. including whoring himself out.