This is it. And realize that your bitch factor with said girl is currently through the roof. She could end up boning the bitchiest dude in the world because to her he is less of a bitch than you.
It doesn't take much to jar the "what the fuck am I doing" thoughts in a persons head. Now those aren't thoughts I would get from someone I knew before and and found attractive...but I have been walking home from the bar with a girl I just met and thought about just booking it and running away or making some excuse to get the fuck out of there. And its happened with girls I have ended up in relationships with and really ended up liking.
Girls get those thoughts that turn them off after they know you already, once a girl hooks up with a guy if the dude she hooks up with is desperate it might be tough for her to get rid of him and keep him away from her. Could be because you cracked rude jokes, could be you being cheap, could be anything to flip that switch that makes you unworthy.