Why would a girl CONSTANTLY be curious about other girls in my life?

For starters this girl has a boyfriend that she has been dating for 5 years. I have known this girl for 2 years while working with her. Lately she has been super flirty with me and it seems like she gets super territorial when there are other women with me.

Basically recently I posted a picture where i am sitting with a group of friends and a girl was next to me. Her comment next day was like "i bet you girlfriend is ugly"

Many other times she comments like "who are you texting? your girlfriend?" or "are you going to vacation with a girl?" or "did you go with a girl to the concert?"

Why would a girl CONSTANTLY be curious about other girls in my life?
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