I told him to think about splitting up with his wife, after reading these replies perhaps that was an inappropriate thing to say. It certainly didn't occur to me to tell him to go to the Church for help, what are they going to do? I do honestly think that if he is cheating then surely the marriage is over, regardless of whether he carries on fooling around? But then that is my understanding of how relationships would work, I am aware all religions will work differently.
I don't condone his behaviour, but nor will I be massively judgemental. If there are judgements to be made I will leave that to the higher powers, I am far from perfect myself. The only thing I struggle with is his children, they are the innocent ones stuck in the middle.
One final question, then I promise I will leave this alone. What if he wants to be with this other woman? She isn't LDS, from what I can tell.
Thanks.