Sister invites brother on a vacation to Vegas

My older sister Alex has invited me on a vacation with her to Vegas. It was going to be her and her husband but at the last minute work prevented him from going. Now it's just us against sin city! The first problem, after a long day of slots, poker and some drinking we come back to the hotel room and there's only one bed. The second problem Alex tells me is that the only way she can get to sleep is by masturbating before bed.Maybe I'll just step out of the room. But when my sister takes off her cloths to her tight underwear I hesitate. Its ok bro, it will only take a minute She tells me and hops onto the bed. I'm paralyzed with fear and awkwardness as she spreads her legs and rubs herself moaning and looking at me as I watch. Holy ! She's never done anything like this when we were growing up. She cums, screaming and shuttering.Why don't you masturbate? She asks. It will help you sleep. I tell her that it's ok but she insists. Come on, I'll even help you. She giggles. She pulls down my pants and begins stroking and sucking me. That's it, cum right in your big sisters mouth. She whispers. Her talking like that makes me cum and she swallows with a self satisfied look. I'm speechless as she says. Ok night bro and slides under the covers.