i'm so sorry for you and your situation. i'm afraid i have to agree with lucky. to put your angel through so much agony for such a short life extension just doesn't seem worth it - to him or you. it's always hard to make that decision. we had to have our stray, bandit, put down a few years ago. he had kidney damage from being blocked. we did all we could for him, but he wasn't going to be getting any better and we couldn't stand to watch him starve himself to death (like yours, all he wanted to do was sleep).
please take comfort in the fact that your dear baby lived a good life and that you did everything possible for him. thank god he had you to take care of him! you'll see him again someday - i honestly believe that.