Why does my girlfriend put me down and tell me im a loser after dating for 3 years? ?

during a fight she will take things i say to her twist them up in her head and say them back to me totally different than what i said to her ..example would be .. i say " you shouldnt have drank so much tonight alcoholism starts somewhere...Her response is "your calling me an alcoholic and im doing bad in life but i have all A's and never drink that much ......when all i was trying to say to her was she should watch her drinking not even trying to put her down or call her that at all..she does this with clothes her weight ,her hair,where she lives cause its not as nice as where i live. Then when we argue she will start putting me down even thought im quiet and not even yeling back at her..and she calls me a pussy for NOT fighting someone.which i believe is the right thing to do..cause im in school and about to go to law school in 1 year....when she yells at me and puts me down she brings up **** from the past even though we have DATED FOR 3 years now..i hate argueing i hate conflict and she always end our arguements by saying were done and i cant wait to talk to someone else,i can do so much better than you,your sooo insecure(which i am definetly not im proud of who i am),i need to go find a real man,ive wasted 3 years of my life,i cant wait to be single,stop staying and getting us back together please...theres soo many its CRAZY! Just so you know i have been on vacations with this girl alone,bought her 3 coach purses over 250 each,650 dollar ring,200 dollar ring, so many dinners i cant even count, bought her clothes.....so much stuff..but we have had a mutual relationship she has bought me stuff too but nothing like whati have got her ..not even close! but then she will say im using her for her money WHEN I HAVE MORE THAN HER?? After all the argueing the next day it will be like normal again like it never happened ...??? i am so CONFUSED...??? SHE HAS ALSO TOLD ME SHE DOESNT LOVE ME ANYMORE...but will then tell me the next day i love you but you just upset me sometimes..or she will say were done and attempt to dump me to make me change what im doing that she doesnt like... HELPPP..?? I LOVE THIS GIRL BUT I DONT KNOW IF SHE FEELS THEN SAME ....????