Im confused with my girlfriends behavior?

ok,my girlfriend and i have been seeing eachother for a year and 2 months,but for the last 5-6months,she has been acting strangely,she has a bunch of user accounts for virtual chats,dating services,myyearbook and others,on these profiles she has never,"NOT ONE",changed the status to in a realationship,she talks to alotta guys, gives out her number,and seems really flirty,i keep asking her about the accounts and all she sais is,"i get along better with guys and its none of there buseness,let them think what they want,well...i just recently found a webpage called 43things.com and her name came up under the new years resolution page as,"looking for a vampire",and on there she sais that she's looking for one and hopes to find one soon,sais she's had her share of other men but vampires kind of turn me on....not really but basically saying that,and its dated for febuary of this month,ive been bringin this kind of stuff up to her and she doesnt say much or ignores the conversation and chats to ppl on line,"yeah,uhhuh,ok sure,"and sometimes she even snaps and gits defensive,i really have strong feelings for her and dont want it to end,it ended once a few weeks ago over a guy of course and she called me and basically begged me to go back to her....she didnt cheat that im aware of but i think she's a social flirt online,and over the phone....what should i do..?