Reading unreadable girls?

I like this girl who i beleave is unreadable. She has liked me for 3 years but it was impossible, now we hangout alot but how she acts makes me unsure if she still likes me. The longer I wait the more she flirts with other guys and the more I see her flirt the longer I wait. She still flirts with me but I know she stops acting like this once she has a boyfriend. She throughs out I like yous everywhere even when they hold no feelings so I can't tell if she is serious when I tell her that and she responds the same. She is un readable and never way I've tried I still can't tell if she still likes me. Help.