DEAR HARRIETTE: I have a nephew who is getting married, and he is so happy. He came to me recently to ask for wisdom about marriage, and I fumbled and eventually told him I would think about it and get back to him. I have been married for a long time — more than 20 years — but if I am honest, I cannot say that it is a happy marriage. Sure, we have good times, but we argue a lot and pretty fiercely…