Well i don't think it willbe an ntr but since its classified as drama ,they might show things like splitting or something , like in the chapter where he was in her house ,when he remembered her in childhood and said it was a regret and all , they might show things like him being away frm her and all , who knows,
Although i do fear that the girl might do things which she shouldn't to make him jealous and all
I m really curious what did she say to him that he d say involving with her was a regret