What's the most heartbreaking thing you've ever experienced?

Currently, my sisters decline in health. She's my best friend and we used to do so many things together. Now she's developing horrible neuropathy in both feet, from unstable diabetes. It's not only painful, but because the nerves are dying in her feet, they are numb. She said the numbness is the most awful part. She has to be in a wheelchair chair on the rare occasion we go out. It's breaking my heart so much, and the saddest part is there's no true medicine that works for dying nerves/cure. 😟 She keeps saying she's going to die , or that she wishes she would. 😢