What do I do i About my lying girlfriend?

Shes always broke,yet she works full time and gets child support and money from her rich dad.Yet, she spends $800 /week on new clothes. She lied about having an STD. Shes lies about everything. She lied to me recently about her mom being ill in the hospital(I called the hospital to check on her status),her mom was never in the hospital. She told me not to tell any of her co workers about her toddler son that she has, because she said her coworkers dont know about him, and if her boss ever found out shed be in trouble. She keeps lying about her graduation date from college. The date keeps moving out...she was supposed to graduate this June...Now shes telling me the date is June 2012. Shes lied to me about her getting a sitter some nights. I know all women tell white lies,but it seems like this woman lies every day, and every minute. She told me her dad cut her off financially..turns out he didnt.She tells me she loves her job,next day she hates her job and wants out. Shes lied to me about a nanny for her son. She asked me to get one for her..then i find out she went behind my back and got one herself. Then she denied it when i confronted her. She said" I never ever lie to you". then she cried and said " you dont trust me". But i cant trust when she lies to me. She added me on facebook recently,and i saw so many lies on there that i caught her on. days when she said shes not feeling well to me,shes on facebook telling people she went out drinking hard with the girls the night before. She keeps telling me she wants to marry me, and that she loves me. We have great sex, but the lying is really taking a toll on me.She also lied to me about her brother being in the hospital recently. I threatened to break it off last week, she then called me crying saying she didnt want to lose me.She lied to me recently that her mom threatened to throw her out of the house(i was on a busines trip and she called me crying cause she wanted to move in with me in 3 days) I told her no, and she yelled and screamed at me. Well, here it is a month later, and her mom didnt throw her out yet..every word that comes out is lies. She is good with her son and shes a great mom. But she treats everyone else around her like crap including her rich parents. They give her stuff, and she treats them badly. Shes had 3 good girlfriends in the last 6 months shes alienated with her lies,and they dont want to be her friend anymore.I do love her, but i think i need to make a break from this woman.is this compulsive lying or massive insecurity