A guy begins to date a girl & 6 months into the relationship she has video & telephone sex with another guy?

who lives out of state. The guy is currently living in another state.Her bf stays with her and the other guy does not talk to her for 2 months but then reappears & the gf starts talking to the guy everyday. She does not do anything with the other guy just casual conversation. The issue for the bf is that she is talking everyday with a guy she has done those things with. So a 3 way conversation is arranged on the telephone and the bf asks the guy & his girlfriend several questions such as "does she like the other guy for more than a friend and she responds "no." The other guy admits openly that her calling him everyday is wrong and that he does not have to talk to her at all and that he can move on with his life. The girl hears this clearly. The bf afterwards talks to his gf and asks her if she is going to keep calling the guy and she says she "wants" to call him and that he is just a friend. The bf sees this as a problem. Why does she have to continue to call this guy if the guy blatantly said what she is doing is wrong? The girl says she will "cut back" on calling the guy to 3-4 times per week. The bf thinks this is unacceptable because it is creating a problem in his relationship with her. My questions are: What would make a girl continue to call a guy after he has said what she is doing is wrong in the 3 way conversation? What would make a girl continue to call him when he says he can move on and never talk to her again? What message is this girl sending to her bf by continuing to talk to this guy when her bf has stated numerous times it is creating a problem with him? The girl says that she should be able to talk to her guy friend but the bf says that since she did that with him on the telephone and video then it is a problem. What solutions are available to help eliminate these problems? Thanks