Oh my goodness... I am so sorry for your loss
It sounds like you gave him a great life.
My MIL had a sheltie for many years and had to put him to sleep this year... He had cancer in his anal glands and he went through chemo and surgery and she finally knew it was his time to go.
I cannot imagine how you are feeling right now, just know we are thinking of you...
RIP Sweet Chili