I'm not advocating for any actual cheating or NTR. The reason I brought up cheating is that the MC is young, in school and very inexperienced. At that age, most guys will be pretty immature, insecure and jealous of their partner interacting with other men etc. Which, given that, I was noting that it would naturally cause some fighting between partners and potentially others. I'm not saying it should be constant, just one part of the story.
Also, this clearly isn't a 'loving well established couple explores sharing together in a mature and healthy way' kind of story. This is a story about a brand new relationship that, almost from the beginning, his GF is corrupted and acting like a slut. It doesn't mean that the game needs NTR, but to expect a more innocent kind of NTS story is naive in this case and doesn't fit the style of the game anyways.