Interesting, so narrative wise, according to the built-in game world logic, the player who chooses to not share Ain in this situation is being an inhospitable host, and is doing something culturally wrong right?
not necessarily... you can also choose to offer Emilia up for the task (if you got her "early")...
and you can also have Igor sit and watch while you get blown by Ain or Emilia and he gets nothing.
finally, both Igor and Zaton might not get any, if the player so decides...
all options are acceptable in your own domain and you would not be neglecting your guests, who ultimately came for tea, not for an orgy.
If anything, it's the difference between
1)putting a good meal with a fine wine on the table,
2) pulling out all the stops and serving it on your best china, and washing it down with your prize bottle of finest alcoholic beverage of choice.
Either way, you have performed your duty as a host, and good times can be had.
With an old friend like Igor, who isn't at his first visit, there are no obligations or formalities and anything goes, for the entertainment chosen by the player.
Say the event is a formal visit from a higher authority figure, maybe they could try and even ask for the "deluxe treatment" so to speak, (although it could be considered a faux pas)..and it would be up to Zaton to accept the request, to curry favour, or maybe just because he likes the person... or to refuse and/or take offence... but that's not the situation that is presented in the game.
There are a few texts in the library that try to explain the... balancing act that is navigating social interactions and the rules of hospitality in a mostly lawless environment.
If that is the case, is this game, in terms of narrative in its design/writing first, and foremost swing driven when it comes to sexual interactions with other characters male, or female?
nope.. the sex is in many ways a product of the interactions, and not the main focus of the game to begin with, nor is it the drive behind, almost any of the characters and their decisions.
there is no focus on a specific lifestyle, sexual act or kink. Rather, we like to think that we are depicting a world complex enough to give room to most types of sexual interaction.... sex in Zeta is much more freely given, done, taken, enjoyed, but there are social conventions and degrees of status that allow for specific scenes to be showcased.
ultimately, from a sexual point of view, Zeta as a society is the ideal place to depict pretty much any kind of kink, sexual dynamic or variation. swinging as we experience it in our world can be as much a part of it as fostering exclusive relationships, building a harem, trading slaves or whatever have you.
in a way, the player determines a part of it, because he will only ever see the sex occurring either to Zaton or in his immediate surroundings, and since we believe in offering choices to the player, it's him who decides what is acceptable to him and therefore to Zaton... and any choice he makes is acceptable to Zetan standards... which kind of makes it the norm of the game and the setting, at least to the player's experience.