Pain

Levi didn't treat Eren so good once a shocking secret was heard. Eren had fallen for Humanity's Strongest. How did Levi react? He took advantage of it. He made Eren a slave and beated him senseless. Levi, on the other hand, was slowly falling for the Titan shifter. Once Levi has figured it out, he regretted the way he treated him. To be honest, Eren didn't care what happened, as long he was by Levi's side, but that was until he was beaten terribly and used. He was terrified of him, but a little piece of him still loves him.