So sorry for your loss!
My guy is 10 1/2 and I am trying to prepare myself as much as I can. He has hip problems and I know there will come a time and probably without much warning. I'll always have dogs but he has such a personality, there will never be another one like him.
Just be happy you gave him such a good life and he enriched yours. Thats all you and he can ask for. He had a good life when so many of them dont. RIP!