I love my sister. *NSFW*

I'm 15 and my sister is 15 as well, we're Irish Twins but I was born a month before her birthday. She's a girl that's always been in my mind and heart. She's so beautiful, from her dirty blonde hair to her bright green eyes. We've grown up together and I never thought of her as just my sister but like a good friend. She does everything I do, we both like video games and watching anime. In fact she was the one that got me into anime. She's everything I love. I never thought about her that way but yesterday I started thinking about her in a different way. She's always been in my life but I now found her attractive. She's skinny, not to skinny, but you can tell she's small when you hug her with a tight hug and see her little waist. She looks like she's 18 but I assure you she's my age. She's perfect. I don't know how I never noticed it before, maybe I'm just stupid. I've been with girls, I've had sex before but never thought about my own sister. But now I do, I want her so badly. I feel so attracted to her, I can't believe I didn't feel this way before. She's just irresistible. I've been trying to not to think about her that way but it's not working. I want her, I want her bad. What should I do?