What makes a guy jealous and possessive about a girl?

Anonymous
I feel like it doesn't even matter how the guy is when I first meet him, but after getting to know him, he'll turn into this possessive, over protective dude that doesn't like me talking to other guys. So what's the deal? What about a girl makes guys protective and possessive? Even when they aren't even dating? What would make you jealous and possessive?
What makes a guy jealous and possessive about a girl?
28 Opinion