Hi!
sorry to hear about your situation. I only have one O because I wouldn't be able to handle losing one of the little buggers to a fish fight. I'm happy with just one

. That said, I have read many threads about people losing O's to aggression issues in a tank with more then one. Most of them want to go buy a new one to try and replace the old one. I would advise you save yourself some trouble and avoid doing that, I really haven't read about much success with it. Just enjoy the one you have, and He's probably happier now anyways.
How big is the tank?