Sharing A Bed With My step-Sister's Best Friend

I came home late to my best friends house, and since she brought a guest, I had to take the only bed available... the one with her step-brother! She told me to keep my hands to myself, but we were close in the bed, I started to get hot and then I realized how badly I wanted to be close to him... we started to cuddle, and OMG- he got a MASSIVE boner! There was only ONE way to take care of it... DON'T tell my bestie!!!!!