Nothing but a Heartbreak
Zayn and Harry are enemies, so Zayn uses Harry's innocent son Liam as a way to get to him.
Or: Zayn and Harry are both the bosses of rival companies. They went to school together and were never friends, always competing and trying to outdo each other.
Zayn wants to hurt Harry and make him suffer, and he realises that nothing is worth more to Harry than his precious son Liam. So, he makes the young boy suffer by loving him and then breaking his heart.
But what if Zayn falls in love too?
Idea credit goes to @xzixamx