@Hiraelle I'm really bad at that, but honestly, to me, that was obvious in season 3
The way they're looking at each other when they're making fun of their ex-boyfriend when Korra is holding him in the air
But, the fact that she's the only one she talks to, and even the way they talk to each other, I mean, it would take less to guess they'd fall in love if one of them was a guy
We're so not used to it, even that kind of things seems irrelevant cause we had that for numerous time and nothing ever happenned

But, maybe I knew it cause someone told me there was a couple of two girls, maybe I wouldn't have guessed otherwise