Maybe jealous isn't the right word.but if your girlfriend is ok sharing you with another girl, you can guarantee she'll expect you to have the same "ok" attitude if she's talking to another guy "friend".
Truth is, I get jealous easily because what's mine is mine. I'm stubborn as hell, I say sorry too much. I act like I don't give a fuck because I care too much. I over analyze the smallest of things & probably come off as a bitch to simply guard myself.