Set: Post reveal, but -volpina(due to cliffhanger), During relationship

Headcanon;

One night, while Marinette's parents are away, Adrien sneaks into Marinettes room, after an argument with his father. When he sees that Mari isn't there, he sleeps in her bed anyway. 

Mari is at Alya's house, and in the morning they drop by Marinetes house. Alya comes up with her, and sees Adrien. Alya naturally screams that Adrien is in Marinettes room, and wakes him up. 

Marinette smiles nervously and tells Adrien off. But Alya is demanding to know, so they explain their relationship to her. Alya then just screeches around for the rest of the day about that.