Responses
Probably the whole thing. He originally was putting up with Mukyeong for the sake of Sunhwa (in secret via sex) and Mukyeong just went ahead and humiliated/ exposed him in front of Sunhwa. Completely ruining their relationship. Making everything Nanjo went through/ and their deal equivalent to nothing.
whats nanjo frustration is it about the last night or the whole sex thing bcz he himself agreed to the deal and wasnt he feeling good ?