how do you know when a girl is flirting with your boyfriend?

So me and my boyfriend have lots of married friends in common, and we've been meeting lately with one couple we meet 6 months ago....  The lady, which is my partner's friend wife, is kind of weird when it comes with my man... She tries all the time to be near to him, she talks to him a lot and other things that are not too obvious but me as woman and girlfriend, feel are kind of weird... What kind of things you think are part of flirting ??? Have you ever had a "friend" that turned out was flirting or wanting something with your so?