BEING JEALOUS?

For some strange reason it seems like people are trying to show happiness for someone by "being jealous" of what they have or what they do.

- I'm going to Spain tomorrow.
- Ohhh I'm so jealous! I wanna go too! have fun.

But, why? In my own little opinion, that's not being happy for someone, it's just being ego. Why do you have to say that you wanna do it too? That's not relevant, focus on the happiness of the other fully instead. I'd rather say "Oh that's gonna be amazing for you, have a smashin' time!!!". But perhaps that's just me.