Don't try to hate yourself like this. You are the way God made you.
And please don't assume that physical intimacy is the only way to show good relationships. There are others. And there is no lesbian look. And whatever you do, God still loves you.
Maybe you're lesbian, maybe you're asexual, maybe you're aromantic. Any one of these things is possible, and many more. But you don't have to figure it out by 17, and you don't owe anything to anyone. Your sister is treating you horribly, and God will make sure that the righteous are uplifted and that the wicked are punished. I don't know if it is sin or not, but no sin can separate you from Jesus Christ's unfailing and reckless love.