Sis Tomi,
Some women give the rest of us a horrible name. I cannot believe this. I would be livid if I were you too!!
I have to agree with what others are saying. The courts do not take nicely to people who are unfaithful and the fact that she left her children with your son will reflect on her if she decides to go for custody. Technically she did abandom them and it is a big deal.
My thoughts are with you and your family. I am so sorry that he has to go through this, but look at it this way at least that horrid woman will be out of his life and he can find someone who will treat him right.

Take care,
Jessica