Ending help thread: http://www.silenthillforum.com/viewtopic.php?t=19989
Basically be overly introverted and/or mean. For the psych profile you'll want to say you're private, don't listen to others' feelings, and don't make friends easily. Don't call extra numbers, and don't answer your phone frequently; ignoring non-puzzle related messages (or maybe you can do it from memory?) may help here too. Calling numbers to see what they say is pretty detrimental to getting this ending. Give Lisa the wrong pills, and when she calls you, slow poke your butt back. I think you can get points for this ending by not watching John and Michelle's little scene in the car, but not sure.
You don't HAVE to be a jerk to get this. If you're so Cheryl-centric that you keep to yourself you can get this, but being a jerk makes it easier. Not that I know why you'd want this ending D=