I stopped playing this a while back because I'll play a game for a bit, go to another game, and so on. I haven't played in so long, I forgot the premise of this, so I restarted. I'm now back where I was and, gotta say, this is one of my new favorites.
I love the fact the Dev has kept Emma as a naive, innocent girl who hasn't gone "I want the MC to pop my charry" 5 minutes into the game.
Now, I don't know if this is a spoiler or not, so I'll put it in a spoiler line. But, I think, Nate is the stalker. It is just a feeling I have. I could be way off base. But just my opinion.