A few days before today, Bian had indeed ordered his men to investigate Nina's case because the problem was very vulnerable to his relationship with his wife.
Bian doesn't want this problem to drag on, and the media finds out that this will cause Mumut to get colder on him. So he has to move quickly to open Nina's mouth so that suspicion of who impregnated Nina is not directed at him because Nina doesn't want to say anything.
From his subordinates, Bian knows that Nina has been in a relationship with Deo for three months. Whenever there is a time to take Bima out or when he is on vacation, Nina will take the time to meet Deo. That young man even has time to visit Nina at Bian's home.