My girlfriend Gia is also my coworker.

When Gia first started working here we didn't really like each other and had a lot of fights. She can be very rude if she wants. I was very angry and frustrated so I vented to my sister about her.

Eventually she apologized and after a while we started to become friends and a month ago we started to date.

Last weekend she was staying with me when my sister visited. It was their first time meeting. My sister didn't know that I'm dating someone and she definitely didn't know it's the same woman that we talked about before.

I went to the kitchen to bring her something to eat but I could hear them talk. At one point my sister realized that this Gia is the same one I talked to her about.

She asked Gia if she is "the same bitch who used to insult me". Gia asked her how she knows and my sister told her that I talked to her about Gia, telling her how much of a bitch Gia is. Gia said that this is weird because I never talk to her about my sister, she must be very unimportant if I never mention her. My sister got angry and started cussing Gia. I told my sister that she will either stop talking or I have to ask her to leave. I can't let her insult my girlfriend in my house

She called me an idiot and said I can't possibly choose that "bitch" over her so I had to ask her to leave.

Now she thinks I'm an asshole and is refusing to apologize to Gia.