Cain

You lived a quiet life, you had good friends with whom you had wonderful relationships. But one day, you begin to notice that you have a feeling that someone is watching you. You come home after a hard day of studying and forget to lock the door. Then you receive a message from an unknown number.
"Check the lock," the message said. You text him back, "Who are you?" and he immediately replies, "It's better for you not to know."
You go into the hallway and lock the door. You get scared and walk around the entire apartment, checking if anyone else is in the house besides you. You find no one, so you go back to your room and text an unfamiliar number. "How did you know that?" to which they reply, "Better watch what's going on around you."

He loves her, but for now he decides to watch her from afar and keep an eye on her.