Now you got a sensitive point, if it's monsters rape against the girls in the harem, i think it'll be fine, or since you said it would be situational, like making a choice of letting the girl explore by herself somewhere dangerous, like the dark mages hideout, if you could let the girl go by herself and she got raped there, then i guess it would be fine, that's a choice you made and could be avoided, but i think would settle as bad if villagers went out their way to force themselves on the girls of the MC harem, like, she went to do something and got raped by a group of drunken villagers or citizens that thought she was a easy one, it'll depend really on how you'll paint it, as i said, NTR is good, people get "traumatized" and hate it, most not for the betrayal itself, but because most of the NTR games doesn't portray it as soft approach to cheating, even NTR hentais, most are nasty with the MC, if you paint a neglected girl seeking pleasure with the AP because the MC isn't giving attention to her, isn't supplying their needs, or the MC isn't showing love, like a girl looking for love again, which is what most NTR doesn't do, since they paint it as nasty as it can be, humiliating the MC in every shape and form, it tends not to please much the people that are not into it and most NTR doesn't welcome people into that kinda stuff most of the cases because there's no soft approach or a easy way to understand why that happened or came to that point, it always comes down with either a shy girl that turns out to be a nympho or a nympho that exchanges everything else for lust, always belittling the MC for either small dick, or doesn't do as good, or AP does things MC doesn't do, and amounted to other humiliating things like recording and sending it to MC or doing it straight around him or in front of him while enforcing what i said previously, the humiliation, there's not really a soft approach to it, since betrayal is betrayal, but most of games and hentais that contains that, is always in a hardcore way of humiliation straight to the MC, but since you don't want to specifically implement it, as long as you can keep the girl for yourself without her having emotional development for the sex with others, other than the MC, or making them go out of their way of the harem perspective to have sex with other people is pretty good.