I dont know about your state but, in mine it's a no fault divorce state. I had proof of adultry and child abuse on my ex wife but, that didn't matter cause the woman always gets the kids, while the man is financially drained untill they cant fight no more. All i can say to do is to hire a private investigator to follow him and get the proof spending lots of money, or read his text while he is asleep or in the shower. Maybe she doesn't know that he is married? If not I would let her know that he is. If she didn't know then she may be mad enough at him to testify on your behalf in court. Once a cheater, always a cheater but, the funny thing is that the guy that my ex cheated on me with married her and she is doing the same thing to him now!!! The bad thing is, is that a woman can cheat and stay on welfare and collect child support. Not having to work for her money because god give her something that most men cant live without. So, keeping this in mind, I don't think you have to prove much. Not saying your at all like my ex but, women way have an advantage over men in many many ways. The biggest and first thing to worry about is to get checked for diseases if you have had sex with him while he has been with her. I feel bad for you but, all I can say is keep your head up and carefully think things out. Or maybe you could just call the TV show cheaters to get the proof you need.