This has always been my thought of what ereri in canon is (as much as id love levi to be a jeagerist. Alas. It's not real). Levi feeling the ultimate betrayal when Eren leaves him for Marley, effectively breaking Levi's heart. But when they get Eren back, and Levi visits him in his cell, he realizes just how weak for Eren he is. He wants to be mad, furious, heartbroken. But one look into Eren's eyes and all his anger and hurt disappears and all he feels is love and sadness. He thinks about what could've been, what /shouldve/ been. But Eren ruined it when he decided to chose violence and war over their love. Levi drills into him, verbally berating Eren for everything he's done. Meanwhile Eren is stone cold, unfazed by Levi's words, which only makes Levi burn brighter. He lets himself inside the cell so he can get into Eren's face, push him around a little, let his hurt out physically. But Eren's bigger now, and he towers over Levi, grabs his wrists and holds him in place. He pushes Levi up against the wall and leans down, mouths an inch apart. There's nothing but bitter heat and smoke between them. It fills Levi's head, clouding his brain. All he can think about is the feel of Eren's warm skin on his own. It's so familiar, tantalizing, surreal. He missed the feel of Eren so much that when Eren closes the distance between their lips, he gives in to him, forgetting all his anger and hurt. All he can think about is Eren.