He wanted to leave her alone to improve the problem since that's what Charlie's sister preferred. This quote “Leave me alone, Charlie. No, really. What's wrong? You wouldn't understand. I could try. It's just for fun... Do you want me to wake up mom and dad then? No. Well, maybe they could… CHARLIE! SHUT UP! ALL RIGHT?! SHUT UP ! ” (Chbosky 116) reveals how much they care about even trying to talk to their parents about all their problems. Charlie's sister comes to the conclusion that Charlie wouldn't understand his problems and that his parents can't help him even a little. However, she had no other companion to express all her feelings except Charlie, so she decided to tell Charlie everything so that he would drop her off at the clinic. If Charlie's sister had tried to express everything with her parents and siblings with some confidence that they would understand, she might have felt more satisfied or they might have found an improved solution, like talking with the boy who had fun with her by changing her face.