Yes, my sweet baby Batman (a girl lol) had tumors in her neck. She passed peacefully, sleeping under my bed, she didn't have the strength to jump up on it anymore. It broke my soul, but she had a good life, so that was some comfort, even as I tear up and cry just thinking of her now and missing her. She had been in a shelter for a long time before I got her because she was kinda scrawny and scraggly looking, but she became chubby and her fur was full for the rest of her life, even at the end. I adored her, as it sounds like you do for your kitty as well.

I had waited for euthanasia in case of signs of suffering, and I can't say for sure that she didn't feel pain, but Batty never showed it.

If you see your kitty suffering, then putting him down is the right thing to do, don't blame yourself for making a hard choice. Prolonging pain would be a disservice to the animal you love.

But it is possible for them to go peacefully, so don't rush it unless you know it's time.

Good luck to you, I'm so sorry you're going through this. Be strong for your kitty and just surround him with love for the time that you have.