Why is my coworker nervous around me but doesn't talk much when I try to start convos? He will end them abruptly even when HE starts them?

And when i ask him a question like small talk he has ONE WORD ANSWER.

This guy used to hit on me years ago!
Why is my coworker nervous around me but doesn't talk much when I try to start convos? He will end them abruptly even when HE starts them?
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