Julian had been stewing in guilt since he discovered the truth and hadn't been able to say anything to anybody about it. Izzy wouldn't believe him. He didn't know what to say to Roz. So they carried on as they always had while he forced himself to act normally.
He had always been good at hiding his emotions from others because of the way he grew up. Neither of them noticed.
He was still trying to figure out what to do when Roz didn't show up to work. He thought she might be sick at first so he tried multiple methods of contacting her to no avail. Even going to her apartment didn't yield any results. He and Izzy had a spare key in case of emergencies.
She wasn't there but all of her things were, including her purse, phone, and keys. The door had been locked when he came over too so it was as if she had simply vanished.