Many modern writers are moving away from the "misunderstanding" breakup and instead using "differing goals" to create more mature tension.

What do they see in each other that no one else sees? Maybe Character A appreciates Character B’s hidden kindness, or Character B is the only one who can make the stoic Character A laugh.

Before the first date or the first fight, you need two distinct individuals. If they are too similar, they might be boring; if they are too different without a bridge, it’s unbelievable.