Actually thats an interesting concept of meant impostor and horror theme of mental disorders. Especially liked the ending where I first admitted that I'm an impostor and she kills me, and when I open game again yandere reacts as breaking 4th wall, speaking with me personally. That's coolest bad ending, despite I like a good endings for yandere people(I EVEN GOT A TIME TO FIND HAPPY ENDING), always feel wanting to save them, instead of saying how "crazy" they are. Especially, after seeing their suffering(the writer and artists both did a nice job with that, I almost believed in those emotions).
I hope you will go further and make something more big with that idea. Its very atmospheric even being that simple, I even remembered Crimson Gray, which one I guess is worth to mention when you talk about yandere games