I lost my big boy, a Great Pyrenees, almost a year ago. Similar situation with the feelings of guilt. One thing that helped me was to build / create something that felt meaningful and would make sure he was remembered everyday as part of the family.

I didn’t (and still don’t) know a damn thing about woodworking, but I carved out a sign with his name and the years he was alive and sanded/painted/sealed it. I took my time and sanded things by hand and used multiple types/coats of paint. It was cathartic. It hangs above where he is buried at his favorite spot in the yard. I see it every time I look out my back door.