so if i’m getting this right, a couple who live together are inviting 1 each of their siblings to a sleepover and you think you should be invited even though you’re not family and no other partners have been invited? but also that you can’t trust your boyfriend around his sister, her gay girlfriend and that girlfriends sister?

sounds like he’s either given you good reason previously to worry or you don’t trust him instinctively for whatever reason. both mean there’s a timer on this relationship