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.
Then tell Setsuna first.
Dann sag's zuerst Setsuna.
Entonces díselo primero a Setsuna.
Pero díselo a Setsuna.
Dans ce cas, commence 
par en informer Setsuna.
Então diga antes para a Setsuna.