<human>: Had this in break up but I think it applies more to relationship. Im over the break up.

Me[28M] and my ex-gf [27F] dated for 6 years. We hard a few rough patches and breaks. A few months ago she leaves me for another guy. At first I try and convince her to reconsider and that we can work this out. After the conversation she asks for time to consider my words. The next day she sends and email saying "I think its best if we not see each other" and "over time I hope we can be friends" and "This new guy gives her excitement, is really nice"...etc... I call after the email and ask if she's happy. She tells me she is and we have a nice conversation and said goodbye.
Fast forward a few weeks later. I'm at a local pub and run into one of her friends. This friend never liked me and I ask her why. We sit and talk and the friend tells me all the horror stories about me my Ex-gf had told her. I explain my side and bring a little clarity to the situation. Her friend and I talk and drink. She ends up coming home with me. We begin hanging out regularly. Go to shows together.
My ex-gf finds out and calls. She calls me a cheater, spiteful, immature and every name you can call someone. tells me never to contact her again. Between the yelling and "Joe, shut the fuck up or Ill hang the phone up!" and "I hate you so much!" I explain that what Jane and I are doing is our business and its not in spite of her. I apologize and she hangs up.
My question is, if shes so happy with her new guy, the one she left me for, why is this an issue? Why is she not happy for me?

Can you provide a brief rundown of the text in within 3 sentences?
<bot>: Girlfriend leaves me for another guy. I begin seeing her friend. She calls me the devil. Why is she mad and should I break it off with her friend?