My husband and I are in our mid-30s and have a happily open marriage. We date other people casually and sometimes less casually, but it's important to us that the people we see are friends and not just people to fool around with. We've been together for three years and have been open longer than not. We told my pretty traditional friends about the open marriage two months after we started and everyone thought that it was either going to be a passing thing or that it was the beginning of the end of our marriage, but we're happy and our relationship grows stronger all the time. I haven't felt affected or offended by their questions and criticisms and I think that they have a right to voice their concerns and opinions, but since there has been some negativity from them, we've kept most of the details of the dating among ourselves.
We host a party at our home every month. I recently hadn't been able to connect with someone (and their partner) that I see, so I invited them and it quickly came out during the party that that's how I knew those guests. They also brought a friend that they date who I hadn't met before. They may have been affectionate, but I didn't really notice and I personally don't think it makes a difference. Soon thereafter, I overheard a friend of over a decade say that she had to leave because she was uncomfortable with the situation, confirmed that I knew these people through dating, and was out the door minutes later.
I understand that our situation isn't for everyone, but we're all just people and it didn't even occur to me to warn our guests in advance that they might meet strangers from this other part of our life. Should I apologize for putting my long-time friend in an uncomfortable position? It's easy to compartmentalize this part of our life, but if I'm having friends over, I don't really want to exclude some of these great friends that I've made. I'm starting to wonder if I'm going to lose some friends because of this.
You might wanna apologize to your friend—the one who knows you fuck other people but apparently wasn't prepared to meet (or know she was meeting) other people you've fucked—but you don't gotta apologize to your friend.
An apology for the "uncomfortable position" your friend found herself in at your party will help smooth things over and may save this friendship. But more importantly, HI, the convo around the apology will give you an opportunity to discuss your friend's flight response.
You don't mention how many people were at the party... but after realizing you guys had fucked this other couple... and then realizing this other couple brought along someone else they're fucking... and then after the PDA broke out... your friend may have leapt to the conclusion that this "party" was about to turn into an open/poly fuckstorm.
If your friend tells you she fled what she thought was a coming fuckstorm, HI, your good-humored, breezy, upbeat assurances that no fuckstorm was planned that night—and, indeed, no fuckstorm broke out that night—will hopefully set your friend's mind at ease about your intentions and the invitation to this particular party, i.e. you weren't trying to recruit her into your open/poly/fuckstorm "lifestyle." You'll be able to address your friend's misconceptions about open and/or poly folks (we typically don't invite monogamy muggles to our open/poly fuckstorms) and get your non-fucking friendship back on track.
But if the issue was merely knowing she was in the presence of other human beings you and your husband have fucked—if her friendship is really that conditional (condition: she wants to able to pretend you guys are not in an open relationship)—then fuck getting this friendship back on track. Close-minded people make lousy friends generally, HI, but they're particularly lousy friends to people in open relationships.