Fuck me and don't cum inside - my stepsister said this and promised not to reveal my cheating

My stepsister came up to me and said that she knew about my cheating on my girlfriend, but she had an offer for me. I have to fuck her and not cum inside. And so she starts jerking me off, I take off her short shorts, move her leopard print panties to the side, lick her juicy pussy and start fucking her. But in the end I can't hold back and I cum right inside her tight pussy..