<human>: My girlfriend of over a year last night called me her ex-boyfriends name in a heated argument. It was obviously a slip up, but what does it mean?

Some context: My GF moved out here to California about 2 years ago. After the first night I slept over at her place after a night of clubbing (2nd time we hooked up) she asked me to jump out of her window because her roommate knew her "boyfriend" from Florida. Before this moment, she had never informed me that she had a boyfriend. (Also, I did not jump out the window). 

Soon after this event, she broke up with him, presumably to be with me. It took me a very long time to trust her because of what happened that night and I let her know that I thought it was extremely selfish that she would date 1 guy and hook up with another. If she didn't want to be with him, then she should have "grown balls" and broken up with him before being promiscuous out here in California.

Either way, after a lot of hard built up trust, we started dating. Like any couple, we have our usual arguments. But last night the argument took a turn when she accidentally was yelling at me and called me her ex-boyfriends name. I was dumbfounded and didn't know how to respond... because I was very unsure as to what it meant! I know if I had called her by an ex girlfriends name of mine, she would have walked out. But I was unsure what to think... so I figured I'd ask the wonderful community of reddit! Thanks!

Can you provide a brief overview of the text?
<bot>: Girlfriend of over a year called me her ex-boyfriends name last night in a heated argument - a boyfriend that lives across the country that she was dating when we started getting involved (that I didn't know about).