pictures help,get him to admit it to you,in an e-mail so he cant deny it. hear say she say is not much in court you need concrete proof.
Talk to him on the phone and reord the conversation sometime where he admits it.
I dont know if he openly admits it to you,my wife did after awhile and was like so get over it,so i had all the proof I needed incase it got that far.
He will wake up one day and realize what he is doing you can not throw all those years away like that.