maybe he is too comfortable around you, Please stop thinking that you are ugly, I't doesnt matter if you are the most beautiful looking person in the world, if he sees you as a little sister or friend figure then he will not see you in any other way. Try to become more unavailable, then he may miss you and realise that you are the one that makes him happy.
The fact that he is looking for a girlfriend, and he has not asked you out, means that he really does see you as his friend, dont worry, if you are the one for him he will not pass you by.
Also you haven't mentioned that you love him, if you love him then tell him, even if he does not feel the same, he will be kind to you and you will have an answer afterwards. Good people dont mess around when it comes to love.