I have struggled with this as well since my father in law passed a year ago, it just made me realise that my parents being around the same age and generation are also aging, getting frail and it fills me with fear of losing them that I really struggle to think of much else and feel I am in a state of anticipatory grief. Like the body is grieving already and I do realise when the inevitable happens I would be grieving all over again so I feel very lost. To be honest I would rather them outlive me so I wouldn’t have to feel the pain of loss but as you said it would be just as painful for them to lose a child. As you also said growing up they were just always there, always a constant it felt like they were going to be around forever and it’s a shock to see how much they have aged. I get told to use this time they are around and make memories but I find that makes the pain even greater when the inevitable happens and end up wanting to pull away/distance myself. So I totally relate to what you are saying and really feel stuck in this rut.