My 12 year sister is not interested in me. Am I too ugly?

We are always alone together. She does not look at me, she is always trying not to get to close to me. I’ve never even seen her smile at me in the past year. After our mom and dad are out of the house we see each other. We never have to leave our rooms so we see each other a lot. Do I look so ugly? Or is she scared of me? Maybe she does not see me that way? I’m 17. Honestly, I’d marry her in a heartbeat.<br><br>What’s wrong with me? Why does she not like me?