Why does this girl that is dating my former crush glancing at me in class?

For some reason they sit in close proximity but never directly next to each other even though they are dating. I noticed that she kept turning around to steal quick glances as if she was trying To see if I look at her. Why does she do this and how would she know that I used to be interested in him when I’m not anymore?

Why does this girl that is dating my former crush glancing at me in class?
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