I'm in love with my step-sister.
Why do you love her?
I just can't help myself from feeling this way. I love her.
I can see how this is a tricky situation, but you need to remember that she is family. Even though she isn't related to you by blood, she is still a part of your family and acting on feelings you have is not a good idea. It will make things very awkward for you and your whole family.
I will make it work between us.
There are so many fish in the sea! Why not try online dating and see if there is someone that is a better match for you that you aren't related to.