As we all know, the Survey Corps' number one and number two in terms of force value are mortal enemies.
It is common for people to get into fights if they disagree.
When Lily asked about her relationship with Levi after losing her memory, she always got this answer.
There is no memory and no evidence. This is an unknown love.
They are comrades first, then lovers.
*Bidirectional amnesia plot
*Mediocre little sweet article
Purpose: Most people in the world often cannot help themselves