You sit down, and just look at Jack. You're not sure why, but even with all that's happened, you really really love him. As a dog, you're happy. He's your master, and that's all that matters.
Jack stays asleep, but you feel something switch inside you. Your body shudders, then begins to reform: your fur covered, human-shaped arms, hands, legs, and body reshape. Your fingers become dog's paws, and your hand lengthens as your upper arm shortens. You have dog's forelegs in stead of arms.
Your toes become paws, your feet lengthen as your thighs and calves shrink. You have a dog's hind legs.
Your body flattens and your chest barrels out. Your organs reshape into a dog's.
Your head and ears change into a big, shaggy dog's head.
Finally, you rock back and stick your muzzle between your hind legs to lick at the last of your humanity: your man's penis. You lick it, and it grows larger and redder, then transforms: the sheath stretches around it, and it changes shape to something that looks like red lipstick. As you lick and suck, your very first knot forms at the base of your dog dick, and you come.
Blinking, you realize the transformation is complete: there is nothing left to you that could identify you as a human.
You. Are. A. Dog.
Jack's dog.