You are tormented and confused by what you did and by continuing to be aroused by the thought of it. The sexual feelings that you experienced and the fact that you were not able to resist touching your sister's friend while she slept, suggest that you do indeed need to seek help from a professional therapist.

This one incident does not make you a pedophile. What it does show you is your need to discuss your sexual feelings and thoughts, as well as all other aspects of your emotional life with a skilled, compassionate therapist. Please make an appointment with a therapist as soon as possible.

Use your primary care doctor or your high-school counselor for recommendations if you need help finding a therapist. Once you begin unburdening yourself and sorting out and understanding your feelings with a therapist, you will begin to see the reasons behind your sexual feelings and actions. Let me know when you have made your first appointment.