Is it normal to fuck ur sister

I have a sister name Britney.Shes not my real sister.She is my step sister.See my mom and dad got divorced about 3 years ago.One night they were out at a restaurant.We were sitting in the bedroom watching a show.Then the topic of sex came up.Were comfortable talking about sex.Then see asked have you had sex before.I said yes once.She asked with who?I said with my girl friend.Then she asked do you still have her?No not any more.Then she said do you miss sex?I said yes.Then she said well.....Well what I said?She said shes never had sex before and she wanted to try.So the she asked.Will you?I said sure.Then we tucked in the bed for hours until we could here them in the drive way.But we still fuck away when there gone.Is it normal?