I ruined my girlfriends, best friends love triangle on accident?

I was recently on a double date with my girlfriend of 6 months and her best friend. Her best friend decided to bring a guy around that we hadn’t seen in months while he was over seas. all the while she was dating around to see what she wanted. I was left alone with this guy and asked who he had been seeing, if anyone. Both girls never told me that while he was overseas he thought they were boyfriend and girlfriend. I mentioned she had a friend that I had seen once, wasn’t sure what he meant to her, anything like that. The conversation got very awkward and now I’m the bad guy because later they got into an argument about the guy she was seeing while he was overseas. My girlfriend of 6 months is defending her best friend of 20+ years and I’m stuck trying to figure out how a normal conversation turned into a mess. I feel like I wasn’t communicated with properly to avoid this, and they feel it was none of my business in the first place. Please help.
I ruined my girlfriends, best friends love triangle on accident?
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