Are these signs of jealousy? What does jealousy from a crush usually mean?

Anonymous
Whenever I look or talk to another guy, or a guy says i'm hot, etc... he get's jealous. Like a couple days ago his friend checked me out, stared at me, and said I was hot. Five minutes later, he drove his friend back home (He just brought him to his home). And whenever I mention another friend of his, he get's quiet before giving a one word answer.

Also, when my brother brought over a guy friend to his apartment, he got jealous since he was trying to help me with my crush before. So, my crush thought that my brother was trying to do the same with his other friend.
He was like "So, you know Martin?"
Brother: Yeah, he's my friend
Crush: You know he has a child, right?
Brother: Yeah, but he has problems with his girlfriend
Crush: But he still has a kid

Are these signs of jealousy? And what does it mean when a guy get's jealous over a girl?
Are these signs of jealousy? What does jealousy from a crush usually mean?
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