Is this girl using me for attention?

So I work with a very attractive girl. I kind of like her. She has a boyfriend although she doesn't speak much about him at all. So we tend to flirt around with her a lot, and basically that's mostly our interactions. Sometimes we talk to her about life and out future plans and so on.
She has the tendency to flirt with me, tease me and generally always smiles at me and constantly giggles and laughs at anything I say. She doesn't even mind me taking her hand and drawing on her and so on.
I tried giving her the cold shoulder and talking to her less and avoiding her as much as possible. This resulted in her in sometimes being pissed and sometimes initiating flirting and teasing. One more thing I noticed is that she can get super nervous around me when we are alone.

What do I do?
Is this girl using me for attention?
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