Some of the stuff is highly contradictory anyway. Runah trusts the MC more if he tells her about Alys' attitude (during the end of the first meeting with Det. Grimes), but that will royally piss Alys off. If the MC has sex with Alys and afterward tells Zoey, then she gets pretty pissed off at him; and if he lies, later she learns that he lied (though I don't think there was any stat decrease or anything). There just are enough contradicting agendas and attitudes that I honestly doubt it's possible without, as you said, running into some scenario where you get a game over.
I think the harem tag is because there are certain combinations that seem to be fine. For instance, everyone over at Violet Lips is sexually "freer", so the MC probably could be with Ciara, the twins, and likely others there. Since their allegiance is to the von Rauss clan, it's possible more from that clan could be added as well at some point. Zoey ends up being OK if the MC also has Claire; that might eventually extend further if he has Julie as well, or possibly Anna or something. (It's hard to know in those latter cases, but the first two for sure seem to be fine.) There are probably others as well, depending. But I see no way you could be with all of the possible LIs from every faction in the end.