Her best friend immediatly comes over to thank me for letting her move in and so does the boyfriend. I take a moment, glare at them and tell them to grab their shit.
Hey.this might come from a different perspective,as I was a gf in question and had a guy best friend. It's probably best to trust her, but do let her know that this is.
Her best friend is another girl, and they hang out with each other A LOT, Every time my girlfriend and I start talking or hanging out without her.