The dog appeared very sick at the beginning of the movie and the captions indicate he had to euthanize the dog, "put down", probably because it was ill. I know how you feel +David Choi
since I had to put down my own dog who I only had for 8 months. Cannot imagine what it's like for a dog who has lived with you for a lifetime. If it's any consolation, he looked like he was nearly dead that morning although not suffering. I think you made the right and tough choice to ease his transition.