Hi guys, I just wanted to update this by saying that today was a much better day than I've had in a long time. I took my cat into the vet today, but I did not have him put down. He's still grossly obese and diabetic, but I'm just going to monitor him closely to make sure this isn't a quality-versus-quantity thing. This past week has been absolute hell, and not just with my cat, but with everything in general. This morning when I decided that I had not exhausted every effort just yet, I felt tremendously better. Big Bubba Stewey is doing good too, even though he's giving me dirty looks over his diet diabetes food.
Thank you, all of you.