Not too long ago I began chatting with someone I met in one of my classes. Naturally she's everything I could ever ask for(and more) but she has a boyfriend of a few years. Well, since I have morals I decided to not even bother with her because she has a boyfriend...plus she's the faithful type. But one day my best friend convinced me to pursue her even though she has a boyfriend. He said "Most of the time girls who are unhappy in their current relationship stay in it until they can find someone else". So one day I asked her for her number, and got it.
Now here's where I'm pretty confused. All this week she has talked me into coming to class(i'm somewhat of a slacker). Towards the end of the week I was not only convinced to come to class, but to sit next to her as well. Finally yesterday I went and visited her at her work and waited for her to get off. Afterwards she introduced me to her grandparents and we had a few laughs, then both went home.
I'm just not sure what to think about all of this. I mean, she has a boyfriend but she's obviously shown some interest in me. Its pretty easy to tell since she cutely stutters when shes nervous

Are these signs that she is looking for a replacement boyfriend or should i back down? Remember she's not the "slutty" type of girl...she's generally a good and faithful type of woman. But she flirts with me a lot so it makes me wonder...