Q. My ex and I broke up three years ago. We have a daughter who is now 4. About a year and a half ago, my wife and I had another little girl. My ex is very jealous, and our daughter has told me that her mommy has told her my youngest daughter is not her sister. It’s very confusing for a 4-year-old and I’m appalled that she would do such a thing. I’m not sure how to handle it. What’s good ex-etiquette? A. There is a huge red flag here, and it may not be what you think. I could go on about how selfish and manipulative it is to tell a child an obvious untruth of that caliber, because if it’s trul…