What does it mean when a guy is nervous while talking with you?

I like this guy and he knows. Once I talk with him by chance.. I feel like he is nervous and quckily reacts by his hands when I talk with him, in the next day I see him but he look at all the classmate girls and ingore me (by intent) and his friend was watching me and looking at me.

What does it mean when a guy is nervous while talking with you?
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