Haruki hears about Kazusa's moving from her mother, who she hadn't been on good terms with.  He feels betrayed and angrily confronts her.  But his words force open the door to Kazusa's heart, which she had desperately tried to keep closed so that the three of them could stay together.
That special treatment is why she 
thinks she can get away with this!
Diese Sonderbehandlung ist es, die sie
 denken lässt, sie würde damit davonkommen!
¡Ese trato especial es por lo que 
cree que puede zafarse de esto!
Es ese trato especial lo que le hace 
pensar que puede hacer lo que le dé la gana.
mais à trop lui accorder de traitement 
de faveur, elle prend la grosse tête !
Justamente por esse
 tratamento diferenciado