Your sister recognizes your obsession with your own mother. It's clear. She walks out the door and you're miserable. You look like the world is cruel to not have her in the house for the day. And your sister is here from college to set you straight.

It's impossible to kick the obsession when it's directed at someone who will ALWAYS be on a pedestal. But a sister? No, they won't be put up there ever. You can fuck her. Because when you get to college, all the girls there will be JUST LIKE HER. You'll move on from an obsession with your sister. So... she decides you better fuck her.

And she makes sure it's a really hot time. You'll love it. And eventually... you'll move on from her.