Well, the thing is, chances are you did just about everything wrong regarding this girl
because you like her. You probably treated her too nice, gave her too much time and attention, agreed with her too much and so on.
Unless you're dealing with a seriously emotionally damaged girl (and that's bad news no matter how you look at it), most girls like to date someone who can match them in an argument. Despite what your mother may have told you, there is such a thing as being TOO NICE. If you're always there for her listening to her problems and helping her out, that doesn't tell her you're caring, that tells her you're a pushover. Pushovers make really boring boyfriends.
Maybe an analogy that helped me get into the right mindset will help you as well: a relationship is a bit like a rope pulling contest, with you and the girl holding each end. If you pull to hard (ie. you're a complete jerk all the time) the rope will snap. However, if you don't pull at all (ie. you're a wuss that lives to serve the girl) the rope will lull and she'll find someone who's actually any good at pulling ropes to be with instead... I guess I didn't remember the analogy perfectly, but you get the idea.
Generally if you like a girl specifically, it is a very risky endeavor so you kinda have to know what you're doing. It's probably better not to be too picky at first and just date casually, since otherwise you might pass up a girl that turns out to be your perfect match. I admittedly am the same way though so I don't want to press this point too much.
There's nowhere I can't reach.