Can't figure out how to get that Soo-Ah scene.
You have to do your best to showcase you are available and partially ignore Koko.
If not enough of a hinting, read following guide:
Enter Normal -> Jump in with your story -> Correct her and say you're not in a relationship -> Let the reason linger -> Glance at Soo-ah -> ask Soo-Ah -> Ignore it and go to Soo-Ah