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's not something my best friend's 
boyfriend should be allowed to say to me!
Das ist nichts, was der Freund meiner 
besten Freundin zu mir sagen dürfte!
¡Eso no es algo que el novio de 
mi mejor amiga debería decir!
¡Eso no debería decirlo el 
novio de mi mejor amiga!
que ce ne soit pas le mec de mon amie 
qui me dise ça !
Sabe, isso não é coisa que o namorado