They will always only admit to what has been proven - there is evidence that he contacted these people, but apparently no proof that he acted on it. Let's say there was proof he acted on it one time, but not every other time he made contact - then he would admit it was just one slip up, but only once and never again. The reality is OP will never know the truth but there is enough damning evidence to suggest he has cheated several times that his word is not enough to believe and he probably has acted on it many of those times.