A girl I have been talking to lately is constantly giving me IOIs but once in a while she brings up her boyfriend and it completely throws me off. I have reason to believe that she doesn't even have one at all! I think that she thinks that I want her as a gf and she doesn't want a bf right now so she is removing that as a possibility.

How should you react when a girl is obviously attracted to you but brings up a boyfriend?

Edit: I just want to clarify that she did not bring up when we first met. We studied together several times and texted a bit before she mentioned it.

I found some really good material on this subject posted ThrowawayPUA about a year ago:

I've discussed this in seddit often enough, and it is always accompanied by a bunch of moralizing assholes who think that girls with boyfriends are off limits. So I'll quote a little text I found: AFCs tend to see the boyfriend as a major obstacle or threat in a HB target. However, in the seduction community, boyfriends are seen from a different perspective. To the pickup artist, just because a girl has a boyfriend does not necessarily mean that she is unavailable for a sexual relationship. The important thing to realize is that most girls of quality are likely to have a boyfriend in place before she moves on to another man, or otherwise, she is single for a very short period of time. It is important for a PUA to test the depth of the relationship; at least by understanding her relationship with her boyfriend, and only then make a decision to respect (or not respect) her faithfulness to him. HBs will also often lie about having a BF to dissuade undesirable suitors as part of the UFEA [universal female excuse archive]. Thus, PUAs tend to ignore the statement of the boyfriend unless there is evidence he really exists. Otherwise, most PUAs are generally respectful of established relationships. On most forums, respect of the BF is well understood as many PUAs were once heart broken by a girl who cheated on him. However, the forums and community in general advocate the importance in learning the skill set, while debates on morality ultimately lie with the PUA himself. So, that being said, here is a fairly good discussion of BF Destroyers(http://www.pick-up-artist-forum.com/boyfriend-destroyer-byharmless-vt871.html). There is also a category of AMOG Destroyers, they are of a similar nature in that they are somewhat of a shit test, the AMOG is trying to break your frame. But that is a discussion for another time.