Is it still monogamy?

We've been together since high school. We have a wonderful life together and enjoy a fulfilling sex life. A very fulfilling monogamous sex life. We both have fantasies, watch porn together and we do a little roleplay but there is nothing we would act upon outside of our marriage because that is not who we are. Recently I shared a dream with my wife regarding one if my fantasies it was an interesting twist on monogamy... we went away for a weekend to celebrate my birthday. After an amazing night out we went back to the hotel where my wife handed me a blindfold and said no matter what happens don't take this off. She proceeded to undress me, trading me with little licks, kisses and bites. She sits my naked body on the couch, whispers in my ear happy birthday and kisses me deeply and during that kiss I feel lips wrapping themselves around my cock. I am being kissed deeply by my wife and sucked by another mouth! I'm startled, don't know if I should let this continue when she whispers again in my ear “let it happen” and proceeds to join in on the oral pleasing of me. After I have an incredible orgasm I hear movement and the door close. She removes my blindfold and we then have a longer night of incredible sex.