My thoughts and prayers are with you.
Azodyl is a supplements for pet with kidney problems. Of course this is not a cure and may not even help at all, but perhaps speak with your vet and maybe it won't hurt to give him some
Anti-oxidants & Immuno-stimulants for Cats - Azodyl
...I am giving my two small doses of Azodyl bc they both have crystals in their urine...