DEAR HARRIETTE: I am a 40-yearold single mother of twin 10-year-old daughters. I have been dating a guy for a year. I really like him and even think he could be the one. My daughters, however, have been nothing but nasty to him, regardless of how well he has treated them. He has brought them gifts and taken them to do fun activities, but they still aren't impressed. I know it's because they feel a…