Levi has a girlfriend, Petra, but he doesn't love her. He's always loved YOU, but when he knows you're with Eren, who has exactly the same demeanor as Levi, he tries to stay away. You and Eren aren't really dating, but you both are friends with benefits. Levi wants to break up with Petra, but he doesn't know how. In the evening you're with Eren and doing interesting things. Eren doesn't love you and you too. You're just playing with him, but Levi thinks you're together.