Daniyana where they start as both using each other (both are aware they're being used as such) as someone to be there until their soulmate is. They're not to last, they're meant to ease the yearning off each other, and be a substitute for true love. That substitution becoming romantic love. But neither of them will tell the other, 'knowing' it's one sided. Knowing that they're betraying their actual soulmate. Because one day, Rahne and Kitty will look at them, realise what they truly desire, and come to them. Because one day, Daniyana will separate, no hard feelings, because they don't want each other like that, not really, not at first. And there's no way the other could've fallen into this trap of feelings. So they don't talk about it, they pretend to still yearn for their soulmate, hiding yearning for the person right in front of them. And they're both doing it, oblivious to the other. Until gradually they fall apart, time drifting them apart, feelings they won't touch getting in the way.
And one day, they wake up, far from each other, far from Rahne and Kitty, never having wanted to admit their feelings has changed, their love had redirected. Maybe they realise they made a mistake, maybe they don't, but it hangs over them both.