I think that the way the story is moving and the fact that Daval isn't sure what to do it's proof enough that the whole "monogamy story" wasn't really always part of the plan, but something Daval pushed because was what the subs wanted.
If you ask me, Daval probably wanted to make Daniel fuck the other girls too... again! with Lana as main love interest and probably sharing them with her, since you can do this kind of oedipus story even if the male MC fuck others, especially milfs! this whole "pool party" arc was to test the waters, Daval wanted to see if the subs would accept Sofia and Martha, because it's clearly easier to write threesome/foursomes than write a voyeur story.