Theory time - not sure if other people already said this but yeah just comment if they already did
They are a couple who got stuck in the loop (possibly got into an accident, or possibly in limbo). Got together in high school. Possibly have marital problems or shit like that before they got looped.
If they got into an accident causing the loop, it will possibly explain why they can't remember each other.
They are looping together and resetting, essentially remembering how they were when they were younger and remembering how they fell in love with each other.