I've done a lot of third, fifth and seventh wheeling with my main group of friends - three couples, until very recently. It might be a bit different for me, since we're all individually friends, I'm not just friends with one half of the couple, but for the first few years I felt pretty constantly out of place.
I remember it being very different hanging out with couples in high school, compared to as adults - I think as we got older, everyone got more comfortable in not always having to make sure they weren't 'excluding' their partners by hanging out individually with others. I thi