It looks like you tried your hardest to give him every chance; I'm so sorry it was time for him to go. (((Hugs))) to you and may God comfort you. The time will come (soon, I hope) when you will gain comfort in knowing you gave him a good life and the best in vet care. He couldn't have asked for more.

Godspeed, you beautiful beast. Run in green pastures forever, and enjoy the caresses of your Maker.