longbough

I've had a couple of them in the past. The arrangements usually end when either of us lands a serious relationship/engagement. Usually that's learned when making a booty call - so you end up more frustrated than ever.
One ex-fuck buddy called me a couple of months after she got married. I had to turn her down- I didn't like the idea of treading on marriage. It wasn't easy because we had a long history before she got hitched-up.

A word of advice about maintaining a FB status. Sometimes it's not wise ask too much about their personal life (assuming you both are in different social circles). Such involvement treads dangerously close to BF/GF territory. Unless you are willing to cope with the responsibility of a committed relationship just respect their privacy.
e.g. If they've just had a major breakup or tragedy and called you for sex don't encumber the encounter by asking her to elaborate more on her situation. Just be there and be what she wants you to be. Believe me, you'd want the same courtesy if you had to call her for any reason.