She once thought she could only be his sister, but one day she became his wife.
She once thought that they would always be happy like this, but one day she discovered that she had always been the source of his misfortune.
She once thought she belonged in the position of his wife, but one day she discovered that she was terribly wrong.
He thought he was just her brother, but one day he became her husband.
He once thought that he only regarded her as his sister, but one day he discovered that it was more than that.
He once thought that he could always be in this position of her husband, but one day he found that he had lost his qualification.
They both thought they were supporting actors in this love show, but one day they discovered that they were each other's protagonists.