She splits up with Galen, because she knows she can't satisfy him. Her relationship with her parents also changes, Kirsten hates living with them and lies to them. Kirsten starts to kill after the attack.
Kirsten ends her relationship with Galen due to a lack of fulfillment in their connection.  Her relationship with her parents becomes strained as she finds it difficult to live with them and lies to them. After an incident, Kirsten starts to kill.