Do you ever catch yourself playing favorites with your pets?

I'm sorry to hear that one of your kitties hasn't been doing well! I think in a case like that you are absolutely doing the right thing in putting Oreo's health as your priority. I hope that he gets feeling well soon; it can be hard to see a sick pet going through a hard time.

I've had cases like this where I've had to put one as priority over another because of illness. When my sweet Kikyo got sick, he went from being very energetic and chasing around outside all day long to not wanting anything but to cuddle in my lap and be taken care of. Kikyo was always my little baby; he had been abandoned as a kitten before he was even old enough to leave his mother. I felt like I was truly his mama, and he loved to suckle on my ear lobes for comfort while wrapping his paws around me. He grew up bigger than any other cat I've ever owned, and my grandma was terrified of him! He was harmless though, just liked to play a lot.
He got ill when a disease that was affecting a lot of cats spread through my area. We kept our two cats, Kikyo and Ruby, indoors in hopes that they wouldn't have come into contact with it, but they both fell ill. Ruby was more independent, and wasn't too bothered so long as she was left alone to rest up. She was quite old at that point, while Kikyo was still only 2 years. Old Ruby managed to fight it off, but while we did our best to look after Kikyo, he just couldn't fight it off. It was a very sad time...
That experience, though, was definitely the most time I had ever spent with him, so I am confident that he passed on feeling loved.