Make it an explicitly toxic romance with Luceris trying to forget (a harmful coping mechanism), and the knight enabling him with his, ugh, love. Make the fact that it's a bad, toxic, destructive relationship very obvious in the narrative. Make the knight become progressively more and more delusional (self-gaslighting), and the king more and more of a mess. Drinking. Drugs. Whatever. He's supposed to suffer from the loss of his wife, right? So show that.why the homocidal psychopath of king who married a child has any reason on why he gets to have a relationship with his knight.
Man, all my ideas for ACoAaF can be summed up as "make the story horror-level dark" lol