People generally do not go out alone with the opposite sex when they're committed. Why some members on here pretend this is a awful or a crazy phenomenon is beyond. Its pretty common, its the norm.
Honestly, otherwise is not the norm.
To be fair, this depends on both your social behaviour and how the relationship is born.
My gf and I are antisocial bitches except when we're out together. We met one on one. Dated one on one, etc.
In stark contrast, my ex was a social butterfly and I grew accustomed to her hanging out with a bunch of dudes that were roudy and raunchy but decent enough people all in all.
We met while hanging out with the same group, going to concerts, etc...
I never had reason to be uncomfortable, suspicious, worried, jealous or what have you, but I'm a pretty reasonable guy.
I'm of the mentality that if someone cheats on me, fuck 'em. It's their loss, if it's not my fault. Although, if I find myself slipping and actually hurting the relationship, then yeah, there are grounds for worry; BUT, if you're used to your SO having opposite sex friends then you're only worrying because of what you're doing your relationship.
What do you do then? Start sniffing her blouse for dude's cologne or start getting your shit together as a couple?
You have to know yourself and your SO and be able to read your relationship.
If my GF started doing things out of character (suddenly having new guy friends) without any trouble in the relationship I'd worry, but only just worry. Maybe I should do the same? Maybe I should join her? Maybe sit down and talk?
I can tell you my first instinct won't be asking for advice on a message board.
Sometimes you get cheated on without reason and there's no avoiding it.
Your only consolation is that you out yourself out there. You didn't leave anything up to chance. They weren't true enough or brave enough, or had the moral fiber to break it off before hurting you... which like I said before.
Fuck 'em.
More to your point though, there's no winning formula that the majority of couples follow to avoid worrying and suspicion.
It most certainly isn't forbidding your SO from socializing with the opposite sex right off the bat.
(Sorry for the convoluted rant lol)