Imagine this. You and your boyfriend are out for a drink. He goes up to the bar to get another round. While you’re waiting for him, you get out your phone and start scrolling through Instagram. Your friend has posted a photo from her luxury holiday in Tahiti. You write a comment: “OMG, I’m soooo jealous!” You put away your phone and look for your boyfriend in the crowd. He’s up at the bar, chatting to the totally gorgeous bartender. Even though you know it’s silly, you feel a pang of jealousy.
Or do you? We throw around the word “jealousy” all the time, but, if you think about it, the two cases above are actually quite different. In the Tahiti example, you want to swap places with your friend. You want that island holiday! In the bartender example, you don’t actually want to swap places with her – after all, you’re his girlfriend; she’s a complete stranger. You just feel possessive because she’s chatting to your guy. (You should probably work on that.)
What you’re actually feeling towards your friend is envy, not jealousy. You’re envious because she gets to go to Tahiti and you don’t. On the other hand, your key emotion towards the bartender is jealousy (although you might also be envious of her because she has, say, better skin than you). Jealousy is almost always related to romantic love, and it happens when you feel threatened – when you’re worried someone is going to take away what you have.
But why take my word for it? Here’s Homer Simpson summing it up much more concisely than I have: