I think that one of the ways that inviting others into our bed helped us was that we couldn’t relate to each other in the same old ways we always had (which had roots in societal norms). And even though we’d started with a pretty good sex life, it exploded once we both got out of old lanes and figured out more about what we actually wanted. Don’t have to have a threeway to do that, but in our case anyway, that didn’t hurt!