Do girls have tunnel vision (that is, they usually only crush on one guy at a time)?

If a girl likes a guy, do they usually just crush on that one guy and no one else?

That is what worries me. I think there is this girl that likes me, but I am not totally sure. She has chosen to sit next to me in meetings, and complimented me on my clothes, sometimes we see each other out in the hallways and I have a feeling she might be timing or planning these encounters, but I can't be entirely sure.
Do girls have tunnel vision (that is, they usually only crush on one guy at a time)?
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