My 18 year old dog has reached the end.

Tomorrow, my wife and I are taking our dog to put to sleep. She's just over 18 years old, and has been the perfect example of a pet anyone could have ever asked for. Her mobility has suffered, and she can no longer eat on her own due to her cancer. The last picture is from 15 years ago, when I was 18 and she was about 3. I am heartbroken.