How can a guy like me get with the good girl?

I used to be a loser, in a college full of ***** and bitches, then i met this one (taken) girl, and she introduced me to all her friends, female and male and now im always going to parties and hooking up with girls. i love all of that girls friends, theyre great but not relationship material. ive had one night stands with a lot of them, mostly it was just but ive had relationships wit the nicer ones, but theyre just not the kind of girls who are into relationships and it always ended after a fun few weeks. theres one girl though, shes the only non promiscuous girl (note-i have no problem with promiscuity) and the only one cut out for relationships and i really like her, but ive no idea how to get a girl to be my girlfriend, ive never done it, im good at hookig up but hen it comes to just getting with a nice girl for a meaningful relationship i dont know what to do, and shes so beautiful and sweet why would se go for a guy like me? shes also abstinent and her last boyfrieds have all been jerks that were in it for , so shes very careful around guys and her close friends are very protective. considering my reputation, and my lack of abilty to get with a nice girl,and she fact that shes absolutley stunning ive got no chance