Interesting start, but as the others said the corruption occurs too quickly, and the chaste alternative (not going down the sex paths early on) quickly results in game over for no reason. I was thinking, maybe the guy in the bathroom could pose as an person of interest to the MC, so she decides to befriend him for information. Then he drugs her when she's in a bar (but bring in some stuff so the player can somewhat avoid it, the MC's supposed to be a trained, smart policewoman after all.)
Also, perhaps the drug does wear off allowing the player to not so easily succumb to the sexual path so early, maybe it's an addictive drug, so the player has a choice of giving in to the addiction or fighting it.
Oh, and not sure what you have planned for the non-school sequences, but I'm excited to see more
