Yes, it's realistic. I have friends who attempted an "open" relationship and it lasted only a short time before they split -- the situation was inherently uneven somehow. Isn't it always about someone (usually one party more than the other) wanting to have their freedom but not lose the gift of commitment? How can that work in the long run? However much we intellectualize monogamy into some bourgeois notion that only hangs us up, when it comes right down to it, if you really love someone, you can't bear to see them with another lover. That simple. Now, if it's a relationship of convenience where the couple loves each other but isn't in love, that's a different story and contentment and fulfillment comes in many different forms. Some people are ok with it -- but you can be sure they're not in love.