I cheated on my gf with her sister at her parents house
Why did you cheat on your gf with her sister?
She's totally hot and I couldn't help myself.
Cheating is terrible period, but cheating on your girlfriend with her sister was a really unwise decision on your part. This is going to get you into real trouble in your relationship with your gf.
I know it sounds crazy, but I just stole the sister's sleeping pills and forced myself onto her while she was drugged.
Sexually abusing your gf's sister is completely incorrect and you will need to turn yourself into the police. Think of how this poor young girl will feel when she wakes up and finds out what you have done.