<human>: My ex and I have been broken up since February. We lost our virginities to each other and had been dating for about two years, when he finally decided to end it. Things were getting stale, and I was overly clingy, which I have since realized and changed for the better. Since then, we've still been very good friends. Things haven't been awkward in the slightest-- we both love each others' company. Despite being heartbroken, I don't believe that I could ever live without him as an integral part of my life. 

He entered a new relationship shortly after he broke it off with me. I believe that he dumped me to pursue her, which I am devastated about, but we've still continued to have sex behind her back. Their relationship, I believe, is a more innocent relationship. She is a very sweet girl from what I understand, and I doubt that they've been physical at all. 

The guilt ate me up, and I told her that we had been seeing each other behind her back, to which she told me that she didnt believe me. She pretty much thinks that I'm a psycho ex-girlfriend, trying to ruin their relationship which isnt the case at all. And despite me trying so hard to distance myself away from him, I can't deny that we are still best friends, I am emotionally attached to him, and we are still crazily attracted to each other. He always says things like, "I still find you the most physically attractive", and "You're the only person that I can get so comfortable with". 

I can't stand to think that I still like a guy who is being so underhanded with his girlfriend. I can't stand to think that I am involved in infidelity, am consciously aware of it, but will not do anything. It is totally against my morals, and I feel so selfish, knowing that I am possibly taking away another girl's happiness. The obvious thing to do is to distance myself and cut all contact with him, but my emotional attachment to him won't let me. Any advice?

Condense the text into a few key points
<bot>: I still like and am sleeping with my best friend, despite him breaking up with me and being in a new relationship. I feel guilty, but I dont want to lose him from my life.