I see a possible misinterpretation here...
Feel free to correct me if I am wrong... (the dev, not some rando)
I believe they were trying to give an example of what would make the MC a cuck... not outright stating the MC enjoyed it.
However, as a person who enjoyed this game, and an avid NTR/Cuckold hater, I see nothing wrong with it...
I just see a bitch who is addicted to drugs and bullied the MC's sister, receive karma and falls into depravity and (I just got into this game honestly, don't know much about the future storyline) ends up as the MC's sex slave or smth.