Psychlogical Thriller

I am going to share my idea that I have had in my head for a long time. This idea comes from my experience of receiving numerous misdirected emails, some interesting some not.....

This guy receives these emails that are ment for someone else, he reads them, sometimes laughs, sometimes wonders, but then deletes them. One day he thinks to himself, what if i reply to one of these, just for fun. So he does. He replys and gets a reply back. He takes on the persona of the person the sender is thinking he/she is communicating with. This begins to spiral down, he gets too envolved. Soon he begins to "see" this person at the grocery store, driving next to him, across the street from his house. He begins to to sink into a fog, a delusion, where he no longer can discern between reality and non-reality. At the end of the film, he is dead, from a single gun shot to the head. Was he stalked by this other person and killed? Did he take his own life to escape this bad dream? I guess its up to the viewer to deceide.