He knows that eventually, all people leave, either by force or by will. So when his best friend wants to run away, how is it possible for him to walk away in turn? To be told his father has lost himself a long time ago, and that he has to choose between family or family.
There are bonds stronger than blood; bonds that are as true as shedding blood for another.
Therefore, the arrow he shoots is not a warning, but a farewell and please come back, even if he knows it’s one dream that won’t come true. There’s nothing good about saying goodbye, at least not in the very moment when two hearts part ways.
In actual fact, it feels more like one heart parting ways, and the weakness he feels now is something that will stay with him until it’s his turn to leave and never look back.