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.
The fact that her mother 
lives overseas means there are
Die Tatsache, dass ihre 
Mutter im Ausland lebt,
El hecho de que su madre viva en 
el extranjero significa que puede
Y su madre vive en el extranjero,
À cause du départ 
de sa mère à l’étranger,
O fato da mãe dela viver
 no exterior indica