Why did she get jealous if she has a boyfriend?

Anonymous
I was at the library studying for a test with this girl and one of her friends. She knows I like her but she has a boyfriend so I haven't really done anything about it yet. I was talking to her friend about another class that she's going to take that I've taken before and she asked to get my number. I was about to give her my number but then she was like "hey he's MY study partner!"

So we kind of left it at that and I never gave her friend my number. Why did she get jealous if she's already in a relationship?
Why did she get jealous if she has a boyfriend?
4 Opinion