A credit card statement hidden in the sock drawer. An emailed bill from the MGM Grand when you thought your spouse was on an all-expenses-paid trip. Cheating? Likely, but maybe not the way you think.

DEAR HARRIETTE: My husband and I are going on our eighth year of marriage. Last year, we experienced indiscretion for the first time — to my knowledge, anyway. And as you can imagine, it was hard on ...