Guy's Behavior

Why does my coworker blush around me?

I'm a 20 year old female and my male coworker is in his 30s. We work together a lot and recently I've noticed that whenever we are in a room alone together he blushes bright red. This happens when he speaks to me or when he's staring at me for a while he will blush bright red. I don't see this happening with any other of his work colleagues either

In groups, he is always confident and is always making jokes and he never blushes. But when we are alone together he will blush. Sometimes it will calm down and he will stop blushing but other times he will be noticeably blushing

Why do I have this affect on him?
Why does my coworker blush around me?
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