dude,
I had the same problem back in 2006-20008. Do care of her activities that you don't like the most, like u said she stays late nite, partying, drinking and all ... keep those things in mind.... creat -ve feelings towards her..... I know it takes time but its the best way...
coz if you leave her right away u may not be able to cope with the situations.... be a man.. think of youself... be little bit selfish....
it took me a while too to get rid of her.... when I got rid of her.... she tried to get me back.... but those millions of excuses I had give her already made me feel hate towards her.....
ayway..... good luck dude
once u start feeling -vely towards her.... everything happens automatically...
but first thing is be brave and make -ve attitute towards her.....