Hello, Sharon ...
I can really relate to what you went thru. I discovered my cat, Junior, was having some kidney problems when he was 16 yrs old. I took him to the vet every 6 months to run a test to measure any changes. There were changes, to be sure, but minimal.
About 2 months after a previous checkup -- which was a good one -- I noticed he seemed a bit "sluggish" and not as active as usual (even for a senior cat). Just to be on the safe side, I dropped him off at the vet's after work on a Friday so they could monitor him over the weekend.
I got a call 20 minutes later from the vet. Juniors kidneys had suddenly shut down. The vet had him on a machine to keep him alive. It all happened so suddenly. Long story short, I was given my options and the most obvious and compassionate thing I could do was to have him taken off of the machine. I had to make that decision within minutes. My vet said he was alive but still in obvious pain.
I knew the kidneys problem would gradually get worse over time because of all of the test results but I had no idea when I dropped him off that I'd never see him again.
I'm so very sorry for your loss. I do understand.