How Can I Forgive Myself For Failing My Baby?

It's been nearly three months since I lost my cat baby Rufus and I miss him so bad it breaks my heart. He was only four and I cannot stop thinking that I failed him. I know it's supposed to be a normal reaction to grief but, sadly, in my case it's true, it WAS all my fault. He had been very sick last summer, they said it was a gall stone, but, finally, after a lot of treatment we managed to pull him through. The only trouble is after that I became a bit paranoid and started feeding him less wet food (although it was already diet food), especially after he seemed to develop a bit of diarrhoea (though it may have been me being paranoid again). I was constantly on the phone with the vet, trying new dry food diets, but it never occurred to me to start feeding him more wet food. Eventually, the vet proposed doing some more tests and my baby was diagnosed with triaditis, we tried a number of treatments, but they didn't seem to help either. He stopped eating dry food altogether and would eat even less wet food than I was giving him. We were just about to start some acupuncture sessions and, frustrated with his lack of appetite, I thought it might be a good idea to start giving him boiled meat. I checked with the vet, he said it was ok, so I started feeding him boneless chicken breast. He seemed to enjoy it at first and, thinking it was the healthiest food for him (boy, was I wrong), I gave thim that for about two weeks. I tried tempting him with it even when he clearly didn't want it and only when all else failed did I switch to Hill's id. Again, he seemed to enjoy it for a couple of days, then he wouldn't touch it, in fact, he seemed to have less and less of an appetite and was becoming very lethargic. Eventually he stopped eating altogether, the vet suggested running some more tests and this time they found he had a severe anaemia and his pancreatitis had gotten worse. They got him on iv, I took him for three blood transfusions, after the third transfusion he started urinating blood and died in my arms during the night. Sorry to bore you with all the details, I just wanted to give you a gist of all the things I feel guilty about (there's more actually, but these would be the main things). My question is how can I possibly live with myself after all the stupid mistakes I made, how could I have been so blind and not realize I was actually malnourishing him? How come it never occured to me to try offering him more appetizing foods, even when he stopped eating altogether? I should have researched more about his illness and the proper diet, I should have quizzed the vet more, I should have acted faster when I saw how lethargic he was becoming. I feel I am a terrible person and I will never forget the look in his eyes as life was draining out of him...