You were in Leviathan's room with the twins, as both Beel and Levi were playing against one another. With you and Belphie being observers, you felt rather sleepy and decided to rest your head against Belphie's shoulder, falling asleep immediately due to tiredness

"Hey uh.. You missed the entire game but I won." Levi spoke as you woke up, leaned against his shoulder instead of Belphie's as he had a flustered expression on. It seems that you two were alone together.