When it's just me and my SO, we know who we're seeing and/or where we'll be, so we know ahead of time how to behave with each other. If they're people that we think will understand then we'll go ahead and be ourselves until we notice any 'uncomfortable-ness' then we'll address it, letting them know that our spouses know about us and give them the details that will make them more comfortable. So far so good.
"In a full heart there is room for everything, and in an empty heart there is room for nothing." -A. Porchia