Oh, Aly, I am so sorry for you. You are absolutely right in your decision, as hard as it is to make. You are sacrificing to make sure your animals are happy and I think that makes you a great person. I had a cousin who had two dogs who would get a long for a while, then from out of nowhere the one would attack the other one. Then they'd get along for a while and he'd attack again. The attacks got worse. They were at a loss as to what to do and waited too long in making a decision. The one dog tore the other one up beyond repair and he had to be put down.
You did everything you could have possibly done to try to make these two get along. Sometimes things are just out of our control.
My heart goes out to you.