My heart aches for you and the sadness you feel over what has taken place in your family. i can only imagine how terrible this was for you to live through. you need not feel guilty or ashamed of what you did, it was the kindest act for Arthur and the rest of the fur babies you have. Arthur is at peace now and is not a threat to anyone, anymore. It's going to take time for you to heal as this really isn't much different than losing a pet due to an illness or old age. It all hurts the same. yes it's sad when it's a young dog but you had no other choice. You likely saved a worse situation from happening. Don't be too hard on yourself, you have suffered enough pain already. God Bless and help you're broken heart mend fast.
(((((gentle hugs)))))