Called me his ex girlfriends name

My boyfriend and I have been dating for over 7 months and he called me his ex girlfriends name again last night for the third time since we’ve started dating. They dated for almost 2 years. But he says it’s just a mistake and has no meaning. I feel really weird about it and hurt. I don’t know who to talk to because I’m embarrassed that it’s happened so many times. What do I do?