I am very sorry to hear your loss, RIP Billy !
I can't say I know how it feels, because my dog (Spanish Cocker) is still alive, but very old.. years passed so fast, and I feel I didn't play enough with him...He is already 15 years old, and I heard the average for a spanish cocker is 12-14..
His hair on the top of his head, along with the eyebrows are already white from aging, and he can barely jump in the bed anymore, but he still has that glimpse of happiness in his eyes when he sees me..
Once again, RIP Billy, I am sure he had a good time with you !