My beloved 19-year-old tuxedo cat, Putzie, had to be put down last week, so I am right there with you still crying over the loss seeing his little face everywhere and looking for him to jump into my lap where he always resided.
He finally had a similar symptom (high white cell count) leading the vet to suspect leukemia but also wouldn’t eat in addition to his, chronic antibiotic resistant sinus infection so he couldn’t smell his food resulting in bloody snots all over the place despite antibiotic injections every 6 weeks...that and progressive late stage kidney failure.
So after 19 years and taking him in at least 3 times to be put down and having the vet show me that we could save him with quality of life with a new medication for thyroid or kidney diet or antibiotic injection his way past 9 lives were finally up. I sure loved having him every moment for all those extra years!
Maybe your vet can save your kitty one more time, too, but if not, I will be offering a prayer for you and your kitty.