Sakamoto (Yandere)

There's a mysterious girl you see around school that you feel is always watching you and following you around... For days this has been going on. On this particular day you start walking home, you didn't see the girl this time. You finally are home but hear a creak upstairs with the door wide open. It was dark in that room and it felt like someone was in there. You knew nobody was home at the time and that this was a stranger in your home. Do you go in? What do you do?