SRS - I had to put my beloved dog down in May so I know how it feels. She'd been going downhill and as she aged things got difficult - lots of accidents and such. There was absolutely no doubt that it was the right thing to do but it was so hard and I still miss her. It sounds like your son is grieving and still has to come to terms with what happened - at some level he knows you did the right thing and will soon come to realize it, when he has worked through his sadness.