I'm not quite in my 50's, but will be in a few years.
I have done the marriage/mortgage.
Now single for several years. I've had a very nice FWB for most of years.
As nice as he is to have around occasionally, the thought of living with/trying to build a life together makes my blood run cold (he's half-heartedly suggested it).
He definitely wants all the benefits of a relationship but none of the cooperation.
Has an enormous but incredibly fragile ego.
I hate his sense of 'style' & taste, I admit I'm a snob, but when I put my foot down and insist on a decent restaurant etc he loves it.
I just haven't got the time & energy to put into a project, I've got a young child, my own career, friends/family & creative pursuits which I find much more inspiring if I'm honest. As he is (he couldn't change even if he wanted to, and nor should he) living together would be a step backwards in terms of the quality of my life, my peace & solo time with my child who I adore (2 years old).
A double wage/pension would be incredible, especially in the childcare years, but we'd never agree how to pool our money & I wouldn't want to buy a much bigger house I couldn't afford solo in case it went tits up.
I know women get criticised for being very fussy/too picky, but in my case (& many cases) my life would be worse getting into a relationship with a mediocre man.