Step Sister

I would suggest to find someone else, go out enjoy yourself. I guess your sis doesn't have same thing if she does f her but do not fall hard on her.

And we need a little more info on the situation.

JUST DONT, NOTHING GOOD CAN COME FROM THIS PROBLEM

You should talk to a friend about it, dont tell her or your parents unless you are 100 percebt sure that she is into you too. Try to learn pick up artist/seduction technique to make her like yiu back