This one's a doozy.
We are coordinating apartment booking for our wedding party and some of our friends, and in order to get the apartments, we are doing it 7 months ahead of the trip. One of the groomsmen and one of the bridesmaids are exes, and one of those couples where it's never really over. She asked me originally if he was bringing a date because she wouldn't want to stay in the same apartment if he was. I said I didn't think so, and she went ahead and booked with him. A week later, one of FIs friends asks about apartment stuff, and I told her there might be a spot open in their apartment. and then she tells me, oh that's fun because I want to hook up with him. So I said that the BM was staying there too, and she didn't seem to care, is going to try and wedge her way in, and oh by the way, we've hooked up in the past, but don't tell anyone, especially FI, BM, and GM. Great.
I know I have no right, or energy, frankly, to keep them from sleeping together, but I want to make sure mu BM is not uncomfortable by a living arrangement that she doesn't even know would make her uncomfortable.
Obviously I need to talk to the friend, who has a history of not giving a crap, but I have no idea what to say. Maybe something like: If you are interested in hooking up with one of the groomsmen, please book a separate hotel room, and invite him over instead of making anyone in my wedding party uncomfortable? Does that work? Is it too pushy? Are there better options? We are years out of college. This kind of thing does not happen in our friend group, and I have no idea how to handle it.