Some skepticism is fair, but notice that - because non-monogamous relationships are somewhat socially unacceptable - we'll perceive them to be less common than

Some skepticism is fair, but notice that - because non-monogamous relationships are somewhat socially unacceptable - we'll perceive them to be less common than they are, because people don't talk about them. So randomwalker's situation might be more common than you might think.