hehe, hagatha, you're probably cynical, but in a healthy way.
I think that this might be a bogus post too.
How do you 'accidently' get involved in a group sex situation?
Was there alcohol and/or another drug involved?
How did it occur?
I'm trying to picture this. You're sitting with some girlfriends fully dressed watching tv, gossipping, eating some snacks......OOPS, I'm naked....WHOA, you're naked. Hey, let's just get it on! The rest I can picture in my head just fine *pause to enjoy the visual*
I mean seriously, I'm just curious as to how this would occur.
Now, stop being a dramatic person. You did it, you have a story, get over it. If he leaves, he leaves and he wasn't the one for you. No reason to beat yourself up for something that already happened, although I personally think you wanted it and enjoyed it, but you are having a moral dilemma about it. Just my take.