Ojik Geudaeui Annyeongeul Wihayeo

With her best interests at heart, Ethan decides to let his first love, Ruellie, wed his faithful knight, Zenon. However, on the day she is set to travel and meet her betrothed's family, tragedy strikes and she is found unconscious with her fiancé having gone missing. Ethan saves Ruellie, but upon waking up finds that not only did she lose her memories, she thinks Ethan is her fiancé! Will he be able to right these wrongs by recovering Ruellie's memories and finding Zenon?

(Source: Tapas)