Watching Porn With My Little Step-Sister

My little step-sister is such a princess that she literally wears a tiara. She's daddy's little 18 year old girl and can do no wrong in his eyes. I'm constantly taking the rap for her when she gets into trouble and it's made our relationship a little tense. When I want to relieve tension I'll wait until she's in the top bunk and I'll put on my headphones and watch porn. I've been doing the same routine a few times per week for the last couple of years and never got close to being caught, but tonight was different.