What should i do.?

Okay. i started going out with this guy, Roberto, and i love him and hten i started going out with this one girl. As everyone knows its called cheating. and well we went out for like 2 weeks. and then she broke up with me. I was sad and relieved at the same time because there wouldent be this big weight over my shoulders worrying about when he would fine out. and then she started telling me these things that i dident want to hear. but she just wanted me to realize what kind of guy roberto is. but she dident know that i was cutting myself because of this. the thing that hurt me the most is that she told me that roberto and his ex michelle were meant to be and that we werent. so then i tell her how i feel about what shes telling me and that this was causing me to cut myself and she gets mad.!
and so the next day she is telling my friend cynthia that she has no shame and that she is talking about me behind my back. if she has no shame why couldent she say it in my face. and then she said that she was only telling me this because she cares about me and that she dident want to se me get hurt. so we talk about it and i told her i understood why she told me that. and she said she still loved me and i said i love you and i think thats when she asked me back out. i thought she said something else and so i said yes. and i promised roberto that i wouldent get back together with her. and i did. but i dident even know. until some people asked her if we ere going back out and she said yes.
WHAT SHOULD I DO NOW.!