[CupcakeDolly]

I wouldn't feel bad about it if I were you. Humans are wired to be attracted to anyone who would make a good mate, regardless of their family ties. That's not to say we should go around doinking our brothers and sisters, cuz let's face it, modern society frowns on that sorta thing. It should be a little bit easier not to feel weird about it in your situation, since she isn't related by blood. If I were you, I would let the crush ride out, but not act on it. Chances are it will fade away with time, and you might not want to risk becoming estranged from your family because of it.