Well Korea need China to reunite their country . Without China acquiescence there will be no united Korea.
Right now they are terrified by North Korea owning an atomic bomb. So it is natural they want to protect themselves with THAAD. Knowing well China doesn't like it because it is used as excuse to monitor China missile launches.
But over the longer period their economy need China and you need to brush yourself with Korean History
3 time in the past Korea ask China for help with 1 win(Imjin war), 1 lost(1890's), and 1(Korean war) draw.
Unlike Japan Korea appreciate and value their connection to China in term of culture, language and historical tie.
Just give you and example. Most Korean family name come from China the only true korean family name is Park and Kim the rest are Chinese. They adopted Chines name out of prestige or some even blood tie from the time of Chines suzerainty with many southern Chinese soldier station in Korea.And Korean family are required to provide accommodation and food
The founder of most Korean dynasty are Chinese. Chinese language and calligraphy is highly appreciated in Korea.Legend has it korean come from Mt Paekdu or Changbaixan. Large Chinese korean community in Jilin
Go to Beijing language university there are busload of Korean student literally. They even have korean town