So sad for you and the misses Iddee. After a while they become one of the family. Like children that never leave home. On the positive side the right decision was made and all his pain and suffering is gone.
I can empathize with your loss. A good dog becomes part of you. The loss of a devoted pet it like the loss of a memebr of the family. 12 years is a long time to be together.
Maybe it's too soon to make the suggestion, but how about getting a new dog as a replacement. Start with a youngun and it too will be with you for a long time.