"You're not going, and that's final." Levi means it when he says it. He doesn't want you getting into dangerous work, much less risk your life killing titans.

He's lost a lot of people in his life, far too many to count. He's not about to add you onto the list. You're the love of his life. He'd be damned if something happened to you.

He should've discharged you when he had the chance. If it wasn't for Erwin convincing him to let you stay, he would've kept you far from danger's reach.