[JustAskJulie]

There are no norms, everything varies. While some people like going to clubs with another couple to have a buffer or a comfort zone, others find that doing so creates the atmosphere you experienced where you end up feeling like you are with that couple so you have to stay with THAT couple. It may well be that they didn't expect you to but they didn't say otherwise either so it just happened that way. Remember your primary relationship is what's most important and it doesn't matter what other people think. If you need time alone TAKE IT. If you are feeling a little crowded by the couple you are with just say "hey, we need a little time to ourselves for a bit". No need to be explicit beyond that, you don't have to tell them what you are doing or why.