To my dog,
Hi buddy. I have to tell you something, and I want you to listen closely so you don't forget. Okay?
I'm leaving soon. Soon, you won't see me anymore. You'll feel like something's missing in this house, and you won't quite remember that it's me, but you'll at least know it's something. You may wonder what that closed door leads to, the one that always showed me inside and that you weren't quite allowed in but somehow managed to get up onto the bed of whenever you were welcomed. But then you'll move on to another thought. Or maybe you'll notice that the person who always kissed your head at night has disappeared, but maybe you'll be thankful; thank God you don't have to put up with that anymore! I always thought you kind of enjoyed my kisses, but even if you didn't, at least you knew how loved you are.
Your tummy rubs will happen less often. Sorry to tell you, but I'm the one who gives them to you the most, and when I'm gone, well, don't expect Mom and Dad to make up for it. And there may be less food accidentally dropped on the floor for you; they're a lot less clumsy than I am, for some reason. It's okay, though. You can always sneak some of the cat's food, if you're quiet about it. They'll never know.
I'll miss you more than you'll miss me, that's for sure. I'll see something move out of the corner of my eye and assume it's you, then remember you're miles and miles away from me and that there aren't pets allowed in my new home, anyway. Some days I will forget about you, but as soon as I see another dog, I'll remember. I'll pet all the dogs who'll let me, and even some who won't, but they won't be you, and I'll count down the days until I can see you again.
But one day, soon enough, I'll come back. You won't recognize me at first; you'll be so used to the way things have become that an extra person coming in the door will seem threatening. But as soon as I say your name and let you sniff me, you'll remember. And you'll overexert yourself with all the excitement, that I can tell you. You've never been one to let old age get in the way of having fun.
So go ahead. If my door gets left open, somehow, hop up onto my bed. I don't mind. Sneak some extra food from the trash can, or beg for more tummy rubs than you deserve while I'm gone, and see what you can get away with. Distract yourself until I return. I'll be back soon. You'll have to endure my hugs and kisses again, but I don't think you'll mind so much.
I love you.
See you soon, old friend.