Girls, How do I know if my girlfriend has crossed the line with my man?

Ok, I have a question. Here lately, my friend who is a girl is getting very very comfortable with the guy that I am dating. He seems to reciprocate. Do you think this is me being protective and jealous? Am I overacting. I like my friend and I love the boyfriend that I date. How should I handle this. Have you ever had a problem like this, and what did you do. Thanks.

Girls, How do I know if my girlfriend has crossed the line with my man?
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