NTA. But you should consider that she has a boyfriend, and sometimes it could be messy being that awkward situation. And no matter what you do, she is still already in a relationship with someone else.

I've had a similar experience with a coworker where I work. She had a boyfriend, I liked her, I do things for her, hoping she would pay attention to me. But I soon realized that maybe she's using me as something to keep her happy- something that her boyfriend couldn't do. I got hurt but I think carefully about this and see that this won't go anywhere. So I backed out.

I also asked my friends about this and they all have the same response: She's using me to either 1) make her boyfriend jealous so he'd pay more attention to her or 2) She's toying with me to make herself happy while her boyfriend isn't there.