Asking Eric: Son’s falling-out with niece divides family

Dear Eric: My son and my niece had been friends since childhood but had a falling out about a decade ago. She confessed to him that she was cheating on her husband and thinking of leaving him and their 6-year-old daughter. My son suggested she talk to a professional before making a rash decision. She then badmouthed him to everyone else in the family and stopped talking to him for years.