Mine is nice.
We've known each other for years. It's FWBs because we have a lot of mutual friends.
If we ever went official, there'd be way too many people invested in 'oh how sweet...Corvus & FWBbloke!' on the one hand, & disgruntled exes on the other - we are acquaintances of each other's ex spouses.
Both of our marriages have been over for years, long before we started eyeing each other up. But no point causing unnecessary drama.
Plus we both have teenagers, who have busy lives, exams coming up & don't need to be worrying about parental, erm, extra curricular activities.
We have a deal that we'll knock it on the head if either of us start catching feelings. Which seems unlikely, tbh - we've known each other for 3 decades without being troubled by romantic yearnings! Same applies if either of us meets anyone they want to pursue a proper relationship with.
Meanwhile, we grab a takeaway, watch a movie, have a few drinks & go to bed once a month or so, when we're both free for the weekend. We don't go out - that would feel like dating - & we don't chat excessively online in between - it tends to be a 'fancy coming over on Friday? Cool, see you then' level of communication.
It's very very relaxed & suits us both.
If I'm completely honest, though, I know he's keener than I am; not suggesting he's desperate to sweep me off my feet, but he's always fancied me whereas it was a much slower burn from my side. But yeah, so far so good.