Harrasing call

My friend was committed with a boy and they both were good friends and the boy always insisted to go out with him or for a movie but d girl refused many times and their friendship grew in a few months and the won girl's confidence and once my friend went to his house and there they came closer but she said they had hugs and kisses but d the boy being clever on his part and she came to know about this ,by one of his best friends that the boy had kept mobile phones on a separate side and recorded the voice of my friend. Now my friend is confused and mentally very depressed because the best friend of that boy threatened her that he had that voice recording with him too and he will not let her marry and break her marriage. The accepts her mistake because later she came to know that the boy was committed to other girls also and being physical to many of the girls but didn't let her know anything. But the girl confronted the same thing about voice recording with that boy but he pretended to be innocent and said he didn't do any such recording. Now the girl is confused and very much depressed and she is ready to surrender on her part to bring all the truths of that boy and his best friend in front of everyone. Because the best friend of the boy was saying that he would break her marriage. He was also committed to other girls besides being married. But now he is divorced. Pls tell me how to know the truth of them officially and bring it to others. Because my friend thinks that the boy and his best friends are in contact till now but pretending as if there are some disputes between them.