I have had a little experience with this in a couple of ways. When I used to work at a club (where I met hubs by the way) and we were dating, he used to flirt with the girls when he came in, and often was there when I wasn't. This was fine with me as we were nonmonogamous from the very start, but it's true you DO then have to deal with the talking behind your back, the "sympathetic" looks, the "i can't believe he would do that to you" comments--- EVEN when you've made it perfectly clear that it's fine with you and you aren't monogamous. Most people will prefer to believe that you're only saying that to "save face" and that deep down you are truly hurting and upset-- because they would be and they assume everybody else is like them.
And yes, I mostly let it roll of my back, but it WAS upsetting many times not because he did anything wrong but because I then had to deal with the fallout and the fallout was upsetting (and frustrating!) when people won't listen to you and just nod and pat you on the head like you're a child.
For that reason I did make it clear that once I left that job, there would be no dating of people I work with, or flirting around my work place, or anything of the sort. First, if it doesn't work out, I STILL have to work with these people and deal with fallout, and secondly, there are plenty of people in the world elsewhere!
Hubs is also in the military which creates a special set of crazy circumstances. There is a whole undercurrent of cheating within the military families-- on deployments, shore leaves, etc. especially, but not a lot of honest open communication. A lot of don't ask/don't tell, and a lot of "I know he's screwing around, but as long as he doesn't bring it into our home I'll sit here and pretend it's not happening." It goes both ways as well, lots of women alone for 6 months going out together and things happen. So while cheating is known and not accepted, but "put up with" all around-- allowing your partner to see other people is still seen as wierd and sometimes threatening. The other part of this is that if you're at all involved with other military people/families-- it is one of the biggest judgmental gossip circles of crap I've ever seen in my entire life. This is one of the reasons I keep my distance for the most part nowadays, I got caught up in that mess when I was young and I won't go back. But hubs has to be careful where he is now because dating someone would not be seen in the same way due to his career. And again... dating someone he works with could be career-ending if it goes badly and they decide to make a stink, he could seriously suffer.
Anyway, long story, sorry! But my point is that while yes you want to be above board and open-- but you have to take into effect how that's going to affect the other members of your group. I STILL to this day, 10 years later have people who act concerned that I'm still with my hubs-- considering he "was running around on me" back then. Which he wasn't. And they knew that. And they STILL refuse to accept it. :-(