Most people might guess that an affair could cost them large sums of money if it were to lead to a messy divorce, but there are often many other significant cash outlays before divorce is even contemplated.
Forbes has the report: http://www.forbes.com/sites/kerrizane/2016/04/19/how-much-does-infidelity-cost-the-real-dollars-cents/#294a3f9d65db
The Hidden Costs of Infidelity