A million thanks for all the good wishes. Y'all are the best!
The Buddy Cat is improving. Hydration has done wonders, and he's getting medications for the stuff the bloodwork showed wasn't so good. Plus, they're feeding him soft food through a syringe, which he is not resisting, and is now able to keep down.
There are still some pretty serious concerns, though. His doctors believe that he has hepatic lipidosis, which happens when a cat stops eating (significantly or altogether) and the liver tissue begins to convert to fat. Hence, the yellow. They have ruled out all infectious causes (which is unsurprising since he and the Fuzz only see each other and people), but they're still worried about the possibility of the Big C (which I refuse to utter) and, simply, how much damage his liver has taken.
What did help a lot when we visited this evening - because I'm stubbornly guilt-ridden and paranoid, and have thus far been too much of a dumb ass to listen when people who love me told me this - was when the doctor said that we had nothing to blame ourselves for. That cats are notoriously finicky and secretive, and that Buddy probably made it pretty near impossible to notice anything but the weight loss. He also said that Buddy doesn't fight them on the treatment and is, in his words, "a sweetheart." So true. He's always been one to know when people are trying to help him, and he's such a love anyway.
Bryan and I spent quite some time giving our boy cuddles and head scratches. I kept noticing an odd smell that I recognized from the days when my family had dogs that had puppies a lot: animal baby food, of which Buddy had a bit on his paws (right next to the yellow tape around the IV line) and face. While he was still clearly drained, he was alert enough to rearrange, plant himself, and nose me and Bryan alternately for petting. I consider this a Very Good Sign.
As for what's next, I guess we wait it out. He probably needs at least a few more days of TLC in the ICU before we can bring him home. I didn't feel up to SnB tonight, but I think I can breathe a little bit more easily, even with the smell of kitty hospital still in my nose.