why are these two hugging

But seriously.
When Althea glimpses the insecurities that Rune constantly hides, she does worry about him, but she can't help him. She is too far removed from his state of mind to understand what he's really going through. She assumes, because he is twelve and she is eighteen, that his dark fears are simple ones that she can illuminate through encouragement, reassurance, and her sage advice.
He may be twelve years old, but being marked for death from the moment you were born gives you fears that won't lift until the mass genocide finally ends. (Or, apparently, when he realizes he has become so strong that there aren't many men alive who could kill him. Which is more or less what happens.)