Is it normal to be attracted to your stepdad/stepdaughter?

Obviously it isn't the social norm for attraction to exist in blended familes. However, this has to be more common than we choose to believe.

My wife and I started dating 5 years ago and have been married for 3 years. She is 38, her daughter is 16, and I am 27, now. There is roughly a decade between each our ages. My stepdaughter and I hit it off from the start. There was never any awkwardness, just an instant friendship. We would watch sports, go fishing, enjoyed the same kind of movies, etc. We had more common interests than I had with my wife. We just bonded.

Few years later, she has matured and is a beautiful young woman. She is top of her class, a home body, no interest in dating, and we are closer than ever.

Here is the dilemma. She has gotten more affectionate in the past couple of years. She hugs me as soon as I come home or just randomly if she feels the need. When we are on the couch she will ask me to rub her feet or calves. Sometimes she will just stare at me and smile.

My wife always joked that she had a crush on me but I always laughed it off. Admittingly, that would be flattering but highly unlikely. I must confess that I have started to notice her as very attractive and share an emotional connection with her that I may never have with my wife. I have always focused on converting that into an appropriate level of love and affection. However, if she were to return those feelings I am going to have to leave. I can't destroy lives and rip apart families. Should I be concerned about her developing inappropriate feelings.