Overall, a well-written tribute to your grief. The only places that I'd urge you to look are the part about the knees and the "I foreseen" I'd change to "I'd foreseen." I see what you were going for with the knees, but the order of lines 2-4 of the strophe feel awkward. If you read just those four lines on knees it sounds as if you have a knee lifting a knee. Take that opportunity to use and describe the hand, that is as emaciated as the knee it's lifting.
Cancer is a terrible thing to watch someone you love suffer with. I'm not sure you ever lose those images, and try as you might to recall earlier days of health, they are jumbled. I sometimes think that you grieve for those memories along with the person.