Certainly one thing I have gathered from these forums is that it almost doesn't matter how Oscar went; the guilt would be there. I have so much guilt about putting Oscar down "too soon," but I also see all these posts about people feeling guilty they didn't put their loved one down soon enough. I agonize over whether Oscar could have had more life, and quality of life as well. The vet gave me some steroids to help him feel better, but that same day I noticed that Oscar just stared off into space and he wasn't affectionate or purring.
I then felt like I was giving him the steroids for me, not for him. He wasn't afraid of death, had no concept of it. He just wanted to be where I was. He could tell I was upset so came to comfort me even though he would have preferred hiding. It's that bond, that connection, that makes me not want another pet. If I see a picture of him, it's a reminder that it's all I have left of him. I miss him so much.
Oscar was but 9. I had not even 4 full years with him. He loved me so much. And I loved him. He is sorely missed.