Sorry for your loss, Niehart.
I don't know what it is that makes the grief so immediate and deep over a dog, but it seems to be common for many including myself.
I like this quote from the author Dean Koontz:
“No matter how close we are to another person, few human relationships are as free from strife, disagreement, and frustration as is the relationship you have with a good dog. Few human beings give of themselves to another as a dog gives of itself. I also suspect that we cherish dogs because their unblemished souls make us wish - consciously or unconsciously - that we were as innocent as they are, and make us yearn for a place where innocence is universal and where the meanness, the betrayals, and the cruelties of this world are unknown.”