Personally, I feel like you're essentially writing 4 vn's. One being the mixed story about the murder and the others being about the romantic interests. If you could find a way to combine the 'dates' and the mystery progressions, you could ease your artwork. For instance, Leighs route has you find evidence that is different to Oscars, but they both lead to the same progression with the mystery. Then, you could actually cut out the mixed sections where you would have to somehow tie it all together again with the others.
Eg. In Leighs route, Oscar and Lucas are nothing more than supporting characters.
Atm, the initial choice of who you interact with after class always leads to the entire group becoming acquainted anyway. You could make it more exclusive
Sorry for the rant lol