
Have I understood something wrong here? Shouldn't it be alright for the two of them to fall in love, as they are the descedants of the mermaid and the sorceress/witch/whatever? If so how is Taeho's behaviour explained in any other way than him not loving the mc? Or were they just supposed to marry in each other's houses but not love each other?

From what I understand, the descendants of the two marry to have offspring, not because of love. If Eunwoo went into the marriage while being in love he would most likely die. Taeho even said himself that he thought that kids their age wouldn't have to worry about being in a pre-arranged marriage or a loveless marriage, but it's a bit of a first for everyone because this time the attributes of being the descendant of the mermaid is shown in a male so it's unclear if marriage is necessary since they can't have kids. Idk Taeho's behavior seems possessive since he knows that Eunwoo can't love anyone, including him, without having the risk of death but it does seem like he cares about him to the point of wanting to be the most they can without falling for each other. It might be love or it might just be a sort of obsession/infatuation.
YES, DADDY!
Same lmfao that was exactly me as I read this chapter. "Yes... daddy"