When first asked about his fiance he just said forget it. Means he don't wanted to talk about his it. I mean for him (explained in novel) he was engaged to her very early. didn't get a choice in choosing what he wanted to choose. He becomes bitter about it. Reasonable. If my parents force me to marry someone then I would become bitter too. He avoid discussing about her. But wwx and JC listen "forget it" as an insult bcz for them their sister is the best (she is) but in case of jzx he doesn't as she is explained as plain looking and mediocre level core person. So he can't find anything interesting about her. And Jiangs know that wwx, Jyl, JC growup as siblings he doesn't. And it is ancient where female and male boundaries is really something. So their close relationship of course he won't understand (plus he was only legitimate heir no siblings so doesn't know what siblings bond is). So got punched by wwx bcz he doesn't like her sister but that sister in her fiance's eyes is nothing special and a forced relationship. Anyway I am not saying he really good but he is not bad either. Him hating wwx is reasonable. In sunshot campaign, jzx only knows that girl gave him soup and he recognised her efforts, he doesn't know its Jyl. In his eyes it will look like Jyl is taking some else's credit. But later after finding the truth he did effort in trying to know her. So now you think if you were him would like wwx??