I live in a 4 cat household. We have lived here for almost 4 years at this point. My 3.5yr old cat bullies one of my girlfriends 9yr old cats. Both have been to the vet and have a clear bill of health, but no matter what we do, my cat still bullies hers. Her cat has been around mine for its entire life, I got him as a kitten. They’ve never essentially been friends, but lately he stalks and hunts her through the house any chance he gets. It’s caused my girlfriend’s cat to hide majority of the time. Really looking for any and all suggestions. We’ve tried feliway and it doesn’t help. I don’t need them to be best friends, I just want him to stop being a bully. He gets along with my other cat (his brother) and my girlfriend’s other cat phenomenally, so I really don’t get the issue he has with the other cat. None of the other cats in the house have problems with eachother either.