Has to share a bed with his stepsister and fucks her at night

I came home late to my best friends house and since they had a guest, I had to take the only available bed… the one with my brother! I told him to keep his hands off me, but we were so close in bed that he started to get hot and then I realized how much I wanted to be close to him… we started hugging, and I got a MASSIVE dick! There was ONLY ONE way to take care of this… DON’T tell my girlfriend!!!!!