Sulli and Daehyun were together, until Daehyun asked to break up with Sulli. Sulli was already part of F(x). Sulli was depressed that her   manager would always scold her for making mistakes during practice, f(x) new about her and daehyun, but f(x) couldn't do anything. Until Woohyun came to her life she bagan to put up a real smile and f(x) was happy about it