This study by researchers at Cornell showed that men who earn less than their wives (presumably female) tend have a higher cheating rate, mainly due to feelings of inadequacy about not having the ability to fulfill the traditional ‘provider’ role for men. On the other hand, women who earn less than their husbands are less likely to cheat because they go through a logical thought process which tells them that it is not worth the consequences. If only men were that smart.
Of course, as it turns out, in any case where either spouse earns significantly more than the other, cheating is more likely for the big money spouse. Apparently, this is because high incomes provide the resources needed to cover up affairs. I would add that the ego of many high-income individuals likely contributes to this phenomenon as well.
A case in point where personal ego of a high income individual got in the way of better judgement was Tiger Woods.