Step daughter told her older sister about fucking me

I always figured the older step daughter knew that I was fucking her sister. The older step daughter was not around to much. One weekend she was going to be spending the night and I came home from work and had dinner and went to bed. In a couple of hours the girls came in to say goodnight. The older step daughter asked me how long sister and I have been fucking? I said a few years before mom left she was always jacking me off at night and mom would watch her and mom would tell her to eat my cum and play with my nuts. Then one night mom had her pop her cherry on my hard on. Mom was ok with it? Yes she was. how come I never had any of your dick? I don't know why not. How about now younger sister asked her. Then they kissed and they both were licking my dick. Then oldest one sat down on my dick and she was sliding up and down on it and cuming a lot. Then she started to kiss her sisters pussy. What a night we had and the next morning she said she wanted to spend a week with us. I said ok and she sucked my dick and swallowed my cum load before she headed to her house. I'm looking forward to next week.