I think it's fair to say that social conventions tend to lock some people into relationships that have run their course. In the absence of those conventions, the couple would part amicably and find new, monogamous partners. Because they are bound in a relationship that is past its due date, they start new relationships anyway. If I were a psychiatrist this would be a great model and I think there are plenty of examples of this in the animal world, but I don't know how good a counselor I would be.
Man: "I found out my wife is cheating on me."
Counselor: "That means your relationship has been over for a while. Time to move on."
This is the issue I have with the original article. It says monogamy is rare, when it is actually very common as a biological principle. It points out that animals have multiple partners in a lifetime, but ignores that they tend to be exclusive over long period (say a breeding season.) And while the article says it is not trying to excuse infidelity, it is using this (I believe faulty) premise to avoid pointing out that infidelity is a sign of a significantly decayed relationship, perhaps one that should be ended, not because of this big trust betrayal, but because both partners are no longer committed to continuing.