Why my girlfriend asks me about another guy repeatedly?

I hate to be the bearer of bad news, and this is only my experience as a women myself. Either 1 of 2 things. 1. She is interested if not already involved in him and she is trying to keep you off her tail by showing disgust. This way you will not "worry" about the guy. or 2. She is looking for you to step up to the plate and say something to get him to back off, and let everybody see how much you "love" her. Either way this is not a good thing. The only way to know for sure is to ask her or borrow a friends car she has never seen and go to her job watch and see if something suspect happens. Oh and some women just do love to see their men jealous, for some reason it makes them feel like they care!