Choiza denied of rumors of him and Sulli getting back together through his SNS.
Choiza has recently uploaded pictures of two cats and fans were suspicious. There was a picture of cats in Sulli's SNS in the past. The rumors went viral, and Sulli's recent break up added suspicion. Though there is no way we can know about what happened to Sulli, Choiza and Sulli's ex, we can just assume, Sulli broke up with Choiza because she was in another relationship with her ex, (the boyfriend right after Choiza).
Since Sulli and Choiza showed such sweet pictures while they are together, them being back together and Sulli meeting another man was just a fuzz and a love fight between the two were acceptable. However, Choiza posted the following comment under the cat's picture as rumor spread, They are the babies I raise at home." Another interpretation of the comment, we are not back together.
Sulli is like the Kim Kardashians of Korea, always making an issue whatever she does. However, unlike the long lived issue maker, people are getting pretty tired of Sulli's news and her fuzz. Hope her next news is about something positive.