I completely understand how you are feeling @Nogoodusername. I have been/ am going through something similar. I still find myself dragged back to worrying about my ex on occasions - like when I first posted on here when I found out about his liver diagnosis. Especially because he is the father of my children and I want to protect them - I’m resigned to the fact his life span is severely limited now - and the fact that my children are going to have to go to their fathers funeral at some point, possibly before they finish high school. I look back at baby photos and feel so guilty that this is who I chose to be their father.
BUT, I am so much more detached than I used to be. What helped me was generally putting him out of my mind. I have lots going on and no real room to worry about him too, and any energy I spend there is pulled from things and people that do matter - my kids, my partner, my job, my fitness, my home, my friends - that all deserves my time 100X more. Also years of realizing that whether I worry or not, the outcome doesn’t change. I also wish for HIM that he would recover and not waste his potential….. well he either will or won’t and I can’t control that.
Mindfulness is supposed to help with unhealthy worry because it grounds you in the present, and worry is all about the future - what if what if etc. Worth trying a couple of tracks lying in bed before going to sleep if that’s your thing.
I am also a practical person - so when I find myself spiraling on what would happen in x or y scenario, I get practical. What happens if his liver fails and he is admitted to ICU and given 5 days to live? Well I make a to do list in my head, the people I’d call, the email id write to the school, the time id take off work. I even know how we’d travel and where we would stay, even what I would pack/ wear! Sounds mad, pls don’t judge!
Don't know if any of this helps, but pls know you are not alone.