Why does my crushes friend look at me?

She sits next to my crush, every time I see her friend look at me and I hold for 2 or 3 Seconds on purpose to see if she was really looking and she was. My crush knows I like her bit that was 3 months ago. I left her alone.. I don't know why her friend that sits beside her and hangs out with her a lot look at me... she basically looks at me without emotion.. I know she doesn't have feelings for me but there is something going on.
Why does my crushes friend look at me?
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