Girls, What do you do when you start liking a guy you've known for a while and spoken to him heaps?

This girl i work with has become shy/nervous with me for no reason. She has no reason to be like this towards me. But when we talk it seems slightly awkward. But she has given me a certain look she doesn't give anyone else. This look she has given me is like a smile but her eyes seem to soften. It makes her look more attractive.
Girls, What do you do when you start liking a guy you've known for a while and spoken to him heaps?
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