When Ian Coss talks about the legacy of divorce in his family, he’s not kidding. Everybody split up — parents, grandparents, great-grandparents, multiple aunts and uncles. So when Ian fell in love himself, understanding these broken commitments became his way of avoiding the same fate. Plus, writer and podcaster Christina Tucker on whether universal rules even exist in love and dating. Email us at loveletters@boston.com. (Next episode: Jan. 4)