Tom I am so sorry to hear about Mr. Kitty. He sounds like a cat I would love to have known. I had a similar experience, many years ago -- a mature male Siamese cat walked up on our deck, and let us know that he intended to live here. He was a wonderful cat -- very intelligent, disdained the other cats in the barn but fought with none, came in the house periodically to visit and then asked to be let back out again. He lived here on our farm for the rest of his life. Somewhere along the line, I learned that he had diabetes, and was discouraged by my vet to give him insulin injections. He lived for about another year, and then like Mr. Kitty, I found him out in the barn, having died sometime during the night. For whatever it's worth, your Mr. Kitty's symptoms sound very much like my cat's and so I wonder if Mr. Kitty wasn't diabetic too. It may be something that Siamese are inclined to, I don't know. I've had many cats -- I've never had another with diabetes.
You were very lucky to be chosen by Mr. Kitty, to be his owner. And he honored you greatly by allowing you personal access to him. I hope your sadness is replaced with wonderful, happy memories. And I hope you see him again.