Is it a good idea to keep having sex with someone you used to date?
Is it inevitable that you will start dating again? Or that one of the people will end up hurt or wanting more?
From my (Femanon) experience it really depends on the person.
One ex I had was much more of a alpha-y person. (I say that loosely). I occasionally go sleep with when either of us is stressed. He likes BDSM, I'm a sub. We work well.
The other beta, probably a aspie desu, tried but he got a little clingy and felt really bad about it. I was with him for almost 3 years and he always banged on about how FwB didn't appeal to him BC he wanted the emotions and fluffy shit behind sex.
So I guess its depends on the person. I don't like random sex nor like relationships so this works for me.