Curious of a coworkers actions?

So I'm just looking for opinions and thoughts.

So I have a male coworker that I've sensed for several reasons that he is watching me or tries to hang around my work area often lately.

There has been two different times he has got mad or irritated when I talked to another male coworker.

The first time I talked to the other coworker, this guy gave him the mad look or shut up look and rolled his eyes.

This time when he was talking to me the coworker that seems to get mad, he turned away and walked out and slammed the door.

Now he is being very short and standoffish towards me.

Why would a guy do this?

Curious of a coworkers actions?
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