dog movies can be very, very sad. "Hitachi" and "Racing in the Rain" come to mind. The latter was an interesting little movie about a Formula 1 practice race driver who had a special talent to go for it in the rain. The hero was a dog who talked via Kevin Costner's voice throughout the movie. In the end the dog is dying (age related) and says to his owner "just one more lap around the course, please". Of course I cried ! I read the book beforhand so I knew the end but it was sooooooooo sad anyway. The book is written by the dog too. No kidding.
I'm going through something similar with my dog Pepper who is now 13. Not easy.