Your OTP shares an apartment together but one day they get into a fight and Person A, the more hasty and quick tempered one, decides to leave, claiming that they're moving out.
Two hours later Person B is sitting in the living room waiting for Person A to come home because they know Person A well enough to know that they'll come home eventually.
Bonus: Person A comes home and sheepishly says "...hey, so this is awkward but I kind of left my pajamas here." What happens next is up to you