I fantasize about my friend, is that wrong to do?

So as you can see in the title i sometimes fantasize about my friend who is 2 and a half years younger than me. Im currently 17 and she is 14 turning 15 in two months. So this friend that im talking about is my dad's girlfriend's daughter. When we hangout i feel really attracted to her and i have this feeling that i hangout with her way too much that its starting to be creepy but i dont think that she thinks that though. Anyway i really like her and im kinda stuck because there is a slight possibility that she might become my step-sister one day. Now im not trying to be rude but please dont suggest to just go get her or dont get her, beacause its easier said than done. Instead give me some tips or ideas that i can use to figure out my situation. Thanks

umm.. "easy" has nothing to do with decisions. you either make the right or wrong decisions so drop this idea that it has to be "easy" to do it. all the CORRECT and best DECISIONS are hard to get used to that.

now as to this gal.
1. she's off limits bc she could become your step-sister.. PERIOD. hands off.. look elsewhere.
2. you said "she hardly thinks you're being creepy" which means she doesn't see anything between you two. that why she thinks nothing of it.

this one is really easy in fact.. she's hands off period.
there is no easy or hard about it - just do the right thing period.

The situation is such that you are fond of her. Girl crushes are common at your age, and adult lesbianism far less so. However, you cannot be sure, you may be such predisposed. Try to divert your focus to other girls, that`s just to play safe. Do you best to reduce your exposure to emotional suffering in the future. Girls are fine, but not this one, not under these circumstances. Try to think of her as family already, perhaps your sister, and to mediate your feelings accordingly. To know exactly what your circumstance is right now is actually impossible though. We cannot know what she may be feeling for you but I do n`t see how this enters into the equation anyway.