When a spouse is cheating, they’re either committing adultery or infidelity. The difference is whether you’re married or in a committed monogamous relationship. A majority of private investigators spend their time working on infidelity cases. Washington State is a no fault state, whether adultery was committed or not may be grounds for divorce, but the court is only interested whether one party feels the marriage is irreconcilable. What is important are issues of alimony or child custody.