I am considering doing something kind of grimey in my relationship, I want to know if I should?

I have been with this girl for almost a year. I live in New York, and she does too. However, since January she has been in another state doing a 7 month internship. I went to visit her one time, and during my trip (i can't say i didnt invade her privacy), I discovered that she had lied to me about certain things in her past, and that she basically spoon fed me a image of her that was not true. Through this she confessed that she was indeed a promiscuous woman "in the past" but that she was not since she met me. I also at that time discovered thru the same way that she was talking to this guy while we were already together about all sorts of ual stuff. She even had a plan to meet with him, but I cannot confirm thru what I had that she indeed did. She of course denies that she did, and swears to me that she never saw him and that she has been completely faithful to me. We have been having some problems since those events occurred but are still together. I do indeed love her, and she claims to love me as well. This is where my dilemma comes in. One of her roommates recently moved from the place she is doing her internship at. My girl and the other roommates where not very fond of this roommate but never told her straight up. They even went out to celebrate the day that she left. I am thinking of adding this girl (the roommate that moved) on a social networking site with an anonymous account, claiming im not me, that I am a friend of mine.I want to try to investigate my girlfriend's actions and what she has done over there through that roommate that left. I'm willing to tell her her ex roommates feelings about her to get her to feel comfortable to tell me anything that I should know. I want to know if my girl has been honest with me, or if there are lies to be revealed. Knowing the information at hand, what would you do in my position?