To me it's always a give and take: giving players agency to decide what happens makes it so they in turn feel ownership of the events that transpire. If you can't decide, it's like you are a mere bystander in someone else's story. But if you decide, and as a result NTR happens, it's like "I used my power to make this happen" or "this happened due to my own fault", both things that can be super hot for different types of NTR enjoyers. Personally, if you have 10(+) heroines, if I can "protect" some, that's a small price to pay to make it truly erotic when I "forsake" others - it didn't need to happen, things could have been different, but I made it be this way! That feeling of power, to me is amazing. With great sacrifice comes great reward, as it is said. I understand you don't want to spend time on a vanilla route and vanilla events, but I hope you can give players this "pick and choose who gets it" experience. More than a happy end where not NTR happens at all, it's this chance to avoid NTR with some heroines while having an NTR experience with others that's the ideal/pinnacle of enjoyment for me.