What do you think of the theme: Fire (Katniss) Earth (Peeta) Wind (Gale) Water (Finnick). Did Fire have to end up with Earth?

Well, Gale could be wind. It sort of makes since. Katniss is the fire, and wind fans flames. Like how Gale's hatred for the Capitol helped inspire Katniss' hatred for it. Of course Katniss realized she hated them when Rue died, but it was also like Gale's words about them finally sunk in - so it was like he was helping to fan the flames.

*Sense