Exhibitionist Pack!fic
I’ve been looking everywhere for this fic: it had Derek and Stiles getting into it, and when the pack gets home early Derek isn’t bothered; it’s good for them to see them mate or whatever, and Stiles is doubtful but is too hot to stop. The pack starts getting really into it too because of instincts or something? They don’t join in or anything, but follow them up the stairs to watch through their doorway and are definitely getting off on it. Erica especially, I think. And Stiles likes it, and wonders at the end if he might have an exhibitionist streak. I looked under the AO3 voyeurism tag for so long! I hope you can find it!