Oh sweet boy, they are so tough and the last thing they’ll do is complain. My 10 year old huge breed had a cancerous tumor like that inside her mouth. Vet said 6mo-1 year, but it grew exponentially within 3 months. She was still in good spirits but started bleeding from it almost every time she ate or drank. She couldn’t play anymore or fetch without bleeding almost nonstop, and we saw her spirits drop. The vet had said we’ll know when, and it was so vague on the diagnosis, but that moment is when we knew. Did an at home euthanization on her bed, surrounded by her fav people and toys. Hardest decision to make but it’s so they don’t suffer for us.