2. Monica and the “cheating”
To be clear: there is no NTR in the traditional sense, meaning none of your love interests are taken from you or choose to betray you for someone else. Any moments that seem like NTR (such as what happens in the initial release) are purely for narrative tension. As the player, you can trust that your LIs remain loyal, (unless otherwise directed by you).
This sounds a lot like this will have sharing/swinging/ willing cuckoldry stuff and if that's the case, it would be wise to disclose it from the get go.
You will be surprised to know that people who don't like NTR don't like those tags either.
Again, just asking for you to clarify what's in your plans, not telling you to change anything.
For example, imagine one of your LIs is drunk at a club, and another character tries to make a move on her and she being drunk jokingly flirts back. You, as the player, know she would never actually betray you, but the MC doesn’t have that same certainty. From his perspective, it feels like a genuine threat, and he’s forced to step up, either to defend her or compete for her attention.
If someone makes a move on a LI and she goes along with it, that basically kills her character as a LI. No one likes to be constantly babysitting their women so they don't go around sucking other cocks, they are adults that can make their own decisions so if she decides she wants to flirt back I'm not going to step up or "defend her" . Defend her from what? Herself? She is the one flirting with another man, being drunk is not an excuse, or what, does the mc need to keep her on a leash everytime there's alcohol involved?
That sounds like you are sacrificing these LI, having them act "out of character" for some cheap drama and tension. If she is supposed to be a loyal LI as you describe her then
have her act like that.
There many other ways to build rivalry, tension and conflict in a story, the ntr plot/bait is just the easy one and requires the women to act like whores, when they, supposedly, are not, and the MC to be constantly "saving" them from themselves, that's another aspect people dislike of ntr games so why would they want it in non "ntr games."
BUT, if you are planning to have sharing/swinging/willing cuckoldry then these scenes do make sense, since these "loyal" women would totally be open to fuck others (if allowed by the "alpha"

cuck MC), so them flirting with other men would be fitting, to show they are interested and not entirely opposed to it.
So yeah, it would be nice if you clarify what kind if game you are actually making so you can get the appropriate audience and avoid unnecessary discussions.