As teenagers, it isn't uncommon to fall in love with a movie character and thinking about the actor non-stop. What makes Avatar so special is that it leaves everyone feeling in love.
Not with the actor or actresses, but much more so with the beautiful world it portrays: Pandora!
It isn't uncommon for people to watch the movie and come away with a thing the Germans call "heimweh". The exact translation is "homesick" but it just doesn't carry the same weight as the German version has in german.
Here's how the Urban Dictionary describes the Pandora Effect: