I need advice on how to get my two cats to live together peacefully. They have been living together for 10 years and other than a few dust ups in the very beginning things had been good. Midway has always played so roughly it could be considered play aggressive, and he has always had a high prey drive, so if it runs it is to be chased. However when Montressor had enough, he'd stop and turn and make an angry sound and Midway would stop pestering him immediately. During the times Midway wasn't on the move they showed bonded behavior through mutual grooming.
During the past 2-3 years things have gradually changed. Midway is getting more aggressive in his play, not letting up on Montressor even when Montressor starts growling and hissing. Montressor no longer stands his ground, he runs until cornered. Recently Montressor has started flinching when he sees Midway unexpectedly and the rare times I see any grooming it's two licks and then one cat walks away. Plus Midway is now picking on Montressor if he is wanting something from us (like a walk on a leash).
I've tried territory swapping, I've tried extra attention, I've tried trying to get Montressor to feel more confident, I've tried cat furniture to get extra height. I'm at my wits' end. I'm about ready to get Midway his own cat for a playmate so that he will feel less need to focus solely on Montressor. (Irony, Midway is Montressor's cat so that Montressor could have a playmate back when he was young.)
Montressor and Midway are both neutered males, Midway is 13 (though he bounces off the walls like a younger cat) and Montressor is 20.