These scenes work because they validate the audience's own fears. We have all been in the kitchen at 2 AM asking, "Are we breaking up?" We have all stood at a train station holding a ticket we know the other person won't take. The split scene is the moment the novel breathes real air.
Sometimes a split scene feels static. The solution is the "Third Thing"—an object, sound, or memory that exists in both halves of the frame simultaneously.
Establishing a "missed connection" where characters are physically close but emotionally or visually unaware of each other creates "electric" anticipation for the audience .