I still view The harem as a committed relationship and that the culture and nature of succbi don't matter since their is so many plot points saying that doesn't define them or control them examples the succbus in the tower in stineford going without sex and the two succubus in a monogous relationship, Yelarel going without sex because of her beliefs and Yarra herself going against the incubus king proving that her nature doesn't define her(if they were really sex oriented demons with no autonomy she would have caved) and so many examples...
A relationship can be commited and still be open, the harem can be commited in the sense that they won't leave out of the blue and run off with someone else, but still be open to sleeping with people outside of it. In fact, that is how more people eventually join the Harem, by sleeping with someone that is already part of the relationship (normally Simon).
Also I think there is a big difference between saying that succubus nature and culture "doesn't matter at all" and "isn't the only thing that matters". By the gathering Yarra was already super commited to Simon, but she is also a succubus and she understands that for events like the gathering refusing to participate in the sexual events would mean losing face, specially for a notion as alien to succubi as monogamy is. At no point her intention was to "cheat" on Simon and the sex she had there was just an "activity", as it would be for most traditional succubi events. The fact that she resists the Incubus King shows the difference, the stuff with the other succubi and the orcs was just for sport, but the Incubus King actually wanted to claim her away from Simon, which is why she resisted him with an incredible ammount of willpower.
In lore I believe simon Does get Jealous telling the old man to keep his fingers to himself, Giving Wendis a stare during the dream, and megail Saying "he's possessive but not an asshole" Overall if the people in the harem Wanted to screw other people he would be upset but wouldn't stop them because he doesn't want to control them and wants them to have autonomy in their lives.
In my impression I think the best word to describe Simon would be "protective", he definitely would watch anyone strange approaching the harem like a hawk, but once he asserted that the person wasn't an asshole and that anything that could happen would be strictly consensual, I don't think he would hold any resentment. Not like we can get more than vague guesses since the dev decided to not explore this angle of Simon's personality.
Now I think I can speak for everyone In saying please for the love of everything let this topic die forever lol! This is a tiny part and the Dev stated not wanting to add more its a non issue now...
Yeah, I just want to clarify I have nothing against people that don't enjoy this part of the game, those scenes are far from being my favourites too. But they are a part of the story and, in the story, there's nothing wrong with them, so its frustrating when some people start reading into them like they are being written as cheating fetish scenes or that they mean Simon is an unfeeling cuck or whatever other ridiculous exageration people can take from it. Even more so because one of the themes of the game is to make satire of some rather "entitled" porn tropes, so the fact that the dev decided to concede and not poke fun at this specific type of "entitlement" and moved away from this type of content, only to still have people being upset at it, it really does remind me of the saying "you give them an inch and they will want to take a mile".