Monogamy and Sacrifice

i have a friend, and i heard this about this friend's parents. One of the partners has just decided, we are not going to have sex any more. And can you guess what the answer was, probably not, if they never negotiaed their monogamy in the first place? That strikes me as unfair. But here's the thing, for a lot of people who value the escalator and want the escalator, the idea that of sacrifice is often closely entwined with their idea of commitment. I'm not saying it doesn't matter. Some people, even though that trade often mit be difficult for them, even though it might seem unfair to other people, it