Girl's Behavior

Why does she continue to stare even after she rejected me?

So there this girl in one of my college classes who has been staring at me from the first day. I remember she was in one of my classes last semester but I never really talk to her, she's drop dead gourgeous and while I do consider myself good looking, I don't have much dating experience on the account of that I'm shy so I considered her out of my league. anyways this semester we have been making eye contact non stop and after 3 weeks I (barley) gathered the courage to ask her out and she said she has a boyfriend (Sounded like a lie). Anyways I said okay and shrugged it off, I figured that at least now I won't constantly feel a set of eyes on me watching my everymove and I could start listening to the lecture, but she still stares almost 3 months later! I can't even look towards the area where she sits without making eye contact and she has no reason to look towards where I sit. Even when we have to wait before class she stares. I just don't understand what is it that she wants from me? Does she want me to talk to her? Maybe she thinks I hate her (which I dont?)
Why does she continue to stare even after she rejected me?
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