I'm so sorry for your loss. It's such a hard thing to do. And it's true, they really do help us cope with our stresses in so many ways. Maybe it's time to start thinking about whether you want a new companion.
I found myself, after I put Satin to sleep, intensely missing, not the dog he had been the last two years of his life, but the dog he had been as a youngster. It was really intense for a long time. Even now, two years later, I find myself checking behind my computer chair before I roll back, even though he rarely left the kitchen in the last year of his life. I love my new babies (Harry was around before Satin went, but Cash is only 19 months old), but I still miss my little black monster boy. As you say, 17 years of habit takes a long time to break.
Elizabeth