If you check this forum's history, you will see many came here to mourn their dogs... they are "family" for many years.
they don't last as long as people, but they, unlike people, give ALL their love EVERY day... maybe they know their time is shorter-- or they're just devoid of all the silly behaviors of man, so they just love and expect little in return.
You will know when the time is right... Love sometimes means doing what is RIGHT, not what feels good!
Dogs are people too, we hear, so know there will be remorse, missing and grief after Duffy is gone.
Keep the Son in your eyes!