i’m so sorry for your loss.
I bought my son a dog when he was 6, and clearly needed a sibling. and that’s what the dog was. they played, they fought, they loved. 13 years later, I had to take the dog to the vet to get put to sleep. My son, 19 by then, didn’t want to come.
when I got home, the kid was sitting on the stairs in tears. 6 feet tall by then, he said “I’m very sensitive you know.’
3 years before, we had gotten a second dog, in anticipation of this moment.
As a retired psychologist, I suggest you put a photo with the dog in it in a conspicuous place. There’s been a death in your family. what I found helpful was continuing to talk about the dog, esp memories. talk about how things are sure different without the dog. some things good, some things bad.
10 years later, we had to make the same trip to the vet with the second dog. we were all there, as he died, all around him — my son and his wife. going home, we gathered some photographs and a stuffed toy that looked like Rocky and a candle — we put them together and made a little display. it stayed there several weeks.
it would be helpful to your son if you could use this to help him understand a bit about life and loss — good things happen, and bad things happen, and that’s ok…