What causes a girl ro act quieter towards a particular guy?

She acts quieter towards me for no reason. I've only been nice to her. Nothing has happened between us. Why is she acting like this? 😔 does she dislike me or something. But then she starts small talk with me when we're alone. I managed to get more conversation out of her when I stopped to help her as she fell off her bike.

What causes a girl ro act quieter towards a particular guy?
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