According to the woman's magazine Women Sense's January issue, the pair have been dating for a year and 4 months already. They met in the Summer of 2012, where MBLAQ's G.O introduced them to each other.

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The magazine said, "The two of them mainly dated at the Seoul Hannam-dong UN Village, where So Ji Sub's house is. They had a date on December 19th, and the day after, So Ji Sub dropped Jooyeon off at a hair salon in Gangnam."

The two of them also visited the USA together. Apparently,Jooyeon introduced him to her friends as her boyfriend. 

However, both 51K and Pledis Entertainment said, "This is the first time we're hearing this. We'll be confirming the story."

[UPDATE] So Ji Sub's label has now denied that they two are dating, and has said, "It's true they're friends, but they're not dating."