Maybe his investment is his word: he promised “till death do us part,” and he has no intention of reneging on that. Maybe he’s invested in ensuring that his children are happy and healthy, and he needs their mother to be happy and healthy, too. Maybe his investment is economic: to relieve his own breadwinning pressure as well as pay the bills, he needs his wife’s income. Or maybe he’s invested in his wife’s potential as a human being. Perhaps he understands that her success is his success, and he will do whatever he can to facilitate
