You are not a bad kitty mom. You took him in to get his tooth fixed. If you were a bad kitty mom you'd have said, "Ehh, it's only a tooth, who cares" and left it that way. You love your kitties, and they love you. Stop beating yourself up. Kitties fight, goodness knows my RB Scooter Bug & Charlie fought all the time, enough that I could never leave them in the same room together unattended.

Your sweet Don Juan has my prayers being sent to him for his visit to the vet clinic, and you have them because I know your nerves need calming. ((Hugs)) for you both.