Well I guess Nagumo got what she wanted, somewhat. She definitely broke Shiori with that. I mean it's her father's own fault, but still really sad to see how her father's actions really destroyed a great relationship that she had with him. And for Nagumo of all people to be the witness to Shiori losing faith.
No man, some things can never be undone. They should go their separate ways as Shiori said. Even hoping for them to be regular friends would be too much to ask for after that kind of betrayal.