>>149216266 (OP)Sokka fell for the northern water tribe chief's daughter while he was assigned to guard her.
The northern water tribe got invaded by the firenation and General Zhao made it to the sacred pond where the moon spirit was at.
Zhao killed the moon spirit and waterbenders lost their bending.
The chief's daughter is revealed to have a part of the moon spirit's life inside her after being saved by the moon spirit as a baby.
The chief's daughter gives her life back to the moon spirit, dying in the process but living on as part of the moon.
So Sokka had a girlfriend who turned into the moon.
But Sokka, being retarded, just says it without context in a serious tone. Zuko not sure how to respond to such a ridiculous statement, just nods along and says the line.