How does a guy act when he's jealous that a girl he likes is talking to another guy?

Anonymous
So, there's a guy and I think he likes me...

I'm wondering though, what are signs that a guy is jealous? I never intentionally make him jealous and I never would do that. He works nearby and I am friends with his boss (and that's actually how I met this guy, because I started going over there). His boss is a real friendly guy with a great sense of humor, so he and I are always talking and laughing with each other. Casually of course.

The "boss" and I definitely don't flirt. I'm 18 and this guy is in his late 30's and married with two kids. When his wife is around I talk to her too.

There have been times though that this guy who I think likes me just totally ignores me when his boss is around.

Sometimes the boss and I will be talking and laughing and this other guy will be standing right nearby looking extremely focused and tense. His jaw seems to be tight, his brows furrow, he purses his lips... all, of course, making me think he must be uncomfortable or not okay with something. This guy is usually pretty quiet, but it seems like he gets really different when I talk to his boss.

He won't even say anything to me... he'll just ignore me... I don't know why he would have a problem with me talking to a nearly 40 year old man who is married with kids in a completely friendly way.

What do you think? And also for further reference could you name some other things guys do? Thanks.
How does a guy act when he's jealous that a girl he likes is talking to another guy?
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