Is it normal that i think that my step sister attracted to me ?

So a few years ago, after my parents divorced ,my dad got remarried, and his wife have a daughter of the same age than me, and since i know her I've always be attracted by her, because she's kinda hot, anyway, lately she has been very close to me ( i see her only on vacations), everytime i see her she wants to see a movie with me and stay with me, Yesterday we watched a movie together in her bed and she didnt wear pants :O, we are both 18 btw