Book recommendations for dealing with fear of losing loved ones

A friend I used to be really close with is slowly becoming someone I don’t click with anymore. My dog is getting old and has been losing energy lately, and the same goes for my parents… I keep thinking that I can’t be with them forever, and it’s really upsetting 😢

I’ve been feeling a strong fear about the people and pets I love changing and eventually being gone. Does anyone know any books that might help with this?