Kyung-Soo was happy after receiving Nivritti's message and happier that now he was alone, and Jung-Hwa wouldn't barge in any time soon. After Nivritti did the ceremony to send away the imaginary ghost, Jung-Hwa had been sleeping peacefully in his room and Kyung-Soo got his room back. Well, all got their room back.
Otherwise, Jung-Hwa would barge in whenever he wanted and if he had seen Kyung-Soo jumping and squealing, he would have made fun of him. Not only that he would have babbled about that to everyone.
How he kept hidden the fact that he liked Nivritti was unthinkable. He had no idea that Thae and Jeong-Eun knew about his crush. They were witness to what Jung-Hwa did in that bathroom.
