Sorry about your loss, I feel your pain. I went through the same thing last August with my dog, Eddie. He was 10 when they found a cancerous tumor the size of a grapefruit in his abdomin. I opted for surgery to have it removed but they found it to be tangled up all in his intestines, plus it had already spread all over....nothing they could do so I had to make the decision to have him put down. Although it's been like 7 months, I still get a tear in my eye when I start thinking about him...He was my boy..

Just remember that having the dog put down was the best thing for him.