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.
I can't believe anyone can 
understand him that well after a month.
Ich kann nicht glauben, dass ihn jemand 
schon nach einem Monat so gut versteht.
No puedo creer que alguien 
lo entendiera en un solo mes.
No puedo creer que alguien pueda 
comprenderlo en solo un mes.
Je n’en reviens pas qu’il ait trouvé 
quelqu’un capable de le comprendre en un mois.
Não acredito que  já o entendam
tão bem depois de um mês.