Dear Margo: My girlfriend was in one other serious relationship aside from ours. It lasted three years and ended three years before ours began. She keeps in touch with the ex because they work together a few days a week, and also my girlfriend was close to the ex’s three young children. (They all lived together for most of the three years.) While they don’t spend time together outside of work, once every few months she attends some of the kids’ events (school plays, graduations, soccer games, etc.). I’m not threatened by this, because I have no doubts about the innocent nature of these interactions. Also, the ex is established in a new, seemingly serious relationship.