Very sorry for your loss.
I've been a pet owner all my life, and it's not easy to deal with when it's time to let go.
I have 2 Golden Retrievers now, a 12 year old male and a 10 year old female. The male is really starting to slow down and has gone almost completely blind in the last year. The female is still pretty spry for her age, but she's slowing down too. I dread the day I have to let go of them, they've been 2 of the most loyal companions I could ever ask for.
I've said this for years, and I'll say it again: Mankind could learn a LOT about love & loyalty from a dog.
Take comfort in knowing you gave your dog the best gift you could ever give him: love.