About oxytocin in long term relationships of monkeys

The following information was taken from the book Behave, from the chapter about oxytocin.

There was a study that makes people squirm due to how much it reflects stereotypical human couples. In tamarin monkeys, who also form pair bonds, active grooming and frequent physical contact were indicators of high oxytocin levels in the female partners. And what predicted high oxytocin levels in the males? Lots of sex.