I am sorry to hear you are worried about BaLue. My name is Rebecca. I am a veterinarian and will do my best to help.
When did he last have blood tests, and a urinalysis done? Do you have the results?
In my experience, when a cat stops eating and acts tired of the food they used to like, it is because of some internal disease. In older cats, I rule out liver disease, pancreatitis, intestinal disease like IBD, inflammatory bowel disease (many of our routine blood panels do not give us information about the pancreas, or intestines), heart disease, and kidney disease. Has he been checked for hyperthyroidism lately?
Injections of vitamin B 12 can help with pancreatic and intestinal function, and may improve appetite.
Is he losing weight? Is he drinking any more or any less water than usual?
Let me know about how recently blood tests were done, and a urinalysis; that might be helpful for me to help you. Rebecca