I need help quiting!

Today i have to quit my job...i work for a girl who is younger then i am and shes really nice. The job however, is not all at. I hate it; its peice work and commission...and no paid training. In short, I cannot afford this job and this job cannot afford me. And yet i feel SOOOOOO bad for quiting. Ive been trying to muster up the courage to quit on this girl, and for some reason i cant!!!!!WHY!? I hate this job...but i can't bring myself to quit. I think its cause this girl needs me to further her business, and me quitting will kinda be screwing her over. But then again, i worked 15 hours for free essentially cause she doesnt pay for certain things..I feel bad...but HAVE to do it... here it goes... ahhhh