Don't have any regrets.
This is why i've come to the decision that it is in everyone's best interests for Rudy to be re-homed.
As much as it is upsetting for me, i'd much rather be sad about him having to live somewhere else, than regret keeping him and one or both of them getting seriously injured.
Even with a door between them they are growling at each other, and they have gone for each other on sight.
So i really don't think it will resolve no matter what i do.