I don't want to get into a chaotic argument of you two, but I do have a point regarding this open relationship matter.
This game is plotted on the presumption where the boyfriend enjoy sharing his gf, the gf on the other hand, doesn't have the same kink. There's no reason the relationship has to open on both end for it to be, say, fair, because it's not a competition aboutwho fucks more, it's about a lover do what the beloved enjoys, but within the limits of what him/herself is comfortable about. Because of this, under the context of this story, it's completely different which end the relationship is opened.
If the female protagonist is not willing or doesn't desire to share, like the male pratagonist do, it won't be right to make her to. With that being said, if the game has a different female protagonist, who have the sharing kink at the beginning of the story, we'll have a different premise. But as thing happened, we don't, and it's not a problem, it simply means we won't have a fully open relationship happen at this initial stage of the story, and having a couple as playmates won't make be the best choice. How the bf will be able to make gf agree to share later in the story is a different matter.