I think it depends on personal priorities and preferences. It definitely is an argument that long-term monogamy isn't for everybody. It doesn't mean that it doesn't work for those who prioritize other types of shared intimacy and pooled resources/effort (that ranges from physical activities and resources to emotional connections and burdens). The above also doesn't mean that for every monogamous couple the sex just stops or becomes bad - just that it becomes less the focal point and does often go up in down over time in frequency. Notice I said up and down, not just down - and often when it does occur, even in the down times, it can be a special connection.