Repression

That wasn't the alcohol. You know how much your sister can drink. And she hasn't drank nearly enough to not know what the hell she's doing.

You kiss her back, as she begins to take off her tight clothing. Suddenly it occurs to you that this is right. Your sister NEEDS someone to look out for her, otherwise she'll get into all kinds of trouble. All your helpful actions today have lead up to this moment. The natural progression of your relationship with her. You've always felt that you had a special connection with her, you're her balancer, her anchor if you will. That's why you were so repressed, you felt these emotions were wrong, but now you realize that was just society's rules being forced on you and its apparent that your sister had felt the same way, why else would she put herself in abusive relationships on purpose? She was attempting to run away from her own feelings in a different way. Well no more, tonight you both commit to your true feelings.

You and your sister proceed to make passionate forbidden love in the backseat of her car where you both fall asleep afterwards.

The next day when you wake up you both feel a little weird, but somehow satisfied. You don't say anything to each other, you both just slip your clothes back on and drive home. She holds your hand as you drive, occasionally smiling at you. You're fully prepared to hear Mom bitch at the both of you, but it doesn't matter anymore because together there's nobody that can get in your way.

Yes, its a brand new day, and you feel absolute contentment...
End Of Story