First of all, let me say how sorry I am to hear about your Arthur. I hope he finds the peace at the RB he seemed to be missing here.

Now, let me tell you from experience that you did the right thing. I had to do exactly the same thing a couple of years ago when a dog I rescued (and learned to love very much) bit my daughter on the face. If you think you feel guilty because Arthur attacked Charlie, imagine how you would've felt had he attacked a child and even worse...your child. From everything I've read about your boy, it sounds like it would've happened eventually.

You have absolutely no reason to feel guilty. These things happen sometimes and Arthur knew he was loved. I hope Charlie makes a speedy recovery.