The choices say exactly what they are. (I added the context of the question before the choice)
"If it's within my harem, no [it doesn't bother me if you mess around with other girls]. But not with women outside of it.":
This choice sets lesbian_content = True, which allows harem girls to mess around with each other with the MC not present. They're all still harem girls, though, and the MC is their first priority. The one exception to that is the lesbian couple who will be joining the harem, where the bisexual partner is into the MC, and the lesbian partner is fond of him and wants him to get her pregnant, but she's still primarily lesbian.
"If I am here, of course you can, but I don't want you to do it behind my back. (Do not show most purely lesbian content)"
This choice sets lesbian_content = False, which will, as it says in the choice, hide most girl-girl content, and the girls will not mess around with each other unless in a threesome with the MC at the time.
I 100% trust Vanderer not to include content that involves harem girls trying to make the MC jealous, whether with other harem girls or not, or content that involves harem girls trying to humiliate the MC.
Thanks
Have to disagree that they say exactly what they are. It's a yes or no question with a yes or no answer, both of those answers are kind of yes but with restrictions which makes it confusing. Neither is saying an explicit yes or no. So not something I'd reply with. It's either, Yes I mind or No I don't mind.
So I actually picked the 2nd choice, thinking it was the more obvious one, sure go for it, just not behind my back.
That actually means something completely different from what you've described as it sets it to false.
This means go ahead and sleep with any girl you want, just don't hide it from me. It doesn't mean, I need to be in the room for it to happen, it means, don't sneak around and hide it from me, I want to know when it happens and for you to be upfront with me if you've slept with someone else.
Behind my back means hidden from me. So it means don't cheat, lie, hide, but do feel free to mess around and inform me, up front, not behind my back.
So no, it's not clear as the actual meaning of that phrase is slightly different, but you have cleared it up for me nicely, thank you.
I personally in this situation when writing a choice would always make it unambiguous.
Shag any girl you want, I just want the deets whispered softly into my ear afterwards.
I'd rather you didn't actually, I'm possessive as fuck and want you to be my property, but if I'm there then you may touch.
That sort of thing. Impossible to confuse one for the other.