A New Year's Altercation?

[Journal]

My friend asked me to find her son a math tutor. I introduce her to this guy who I had a great deal of interest in and she knew it. The whole time he was tutoring her son, he stated she was trying to come on to him until she discovered that we were dating because of his constant texting me around her. Even though he stopped tutoring her son that did not stop her from coming on to him. All three of us went out and she tried her best to get his attention. She failed everytime. I enjoyed this because I was beginning to learn a lot about her around men I dated. I decided to go the bathroom and when I got back he was looking a bit confused and uncomfortable. I found out later that she had asked him what he saw in me, how long had we been dating and that she had invited him over without me. He told me he had to decline her. He said he did not find her even remotely attractive after this. He felt she was trying to be deceitful and he felt she was trying to hold me back from having a relationship. My friend guy suggested we not go out anymore, at least not with her, and he would cook dinner at his place from now on. After all she did sleep with my cousin who was engaged to a mutual friend of ours and that mutual friend is unaware this ever happened. Should I remain friends with her, cuss her out and tell her about herself and let her live-in bf know, or should I just walk away and loose contact? Please answer. (Because of serious situation, serious answers only.)