Disclaimer before I get flamed - I love my DH and I love my son and no I do not intend to leave them, and no I am not ungrateful for what I have.
I feel like your fantasy life always differs vastly from what you've got - so when I was single in my fantasy life I was this earth mother with a few precious little children, happy baking and doing craft etc.
Obviously the reality of having a young child bears no resemblance whatsoever to what it was in my head at that point, but there you go.
Now I'm living "that" life, in my fantasy life I'm single and live on my own in a lovely little flat somewhere in North London, which I've decorated exactly to my own taste, and there I work from home and potter about in my little courtyard garden, popping breezily out whenever I please and living in perfect solitude and peace and quiet with my cats.
I feel like this also works with fantasy partners - for example when I was a teenager and I used to go out with bad boy alpha male types I used to fantasise about geeky, intellectual indie boy types. Then when I got older and started going out with that type (and married one of them) my fantasy boyfriend is a brooding, bulky, SAS hitman type of person.
Am I slowly going round the twist in lockdown or do other people have these idle fantasy alternate lives too?