Wrong Name

My boyfriend and I have been together for about 4 months. We've both haven't been in a relationship for 2 years. And we also thought the last persons we were with "were the one." Well we were laying in bed just cuddling and talking about serious things and he said "Meghan look..." I don't even know what he said after that, but I interrupted and said excuse me, while taking his arm off me. AND he didn't even realize he had called me his ex's name. I was so mad and honestly it still has me ticked off. Should I feel that? If they had such a terrible relationship and she treated him so bad, then why would that even be a mistake?