Trying to help out a friend

What is the name of your state? Illinois

I live in the state of Illinois. A friend of mine is married and her husband is supposed to be attending school. They have 2 children and they only way she can contact him is through e-mail. He has been attending school for a total of about 3 years now and was in a lot of organizations that traveled to different states. He came home from one of his trips with another woman to stay in the house they had built. Now he has changed schools, she has no way of getting in contact with him, and doesn't call unless it is convienent for him. Now he wants to take the children, not his wife, to where he is living to stay with him for a week. What should one do in a situation like this. I know this is really long but she needs help and she isn't a very aggressive person. Also what type of legal advice could one possibly give so she can maybe file for a divorce and not loose everything she has.

Thanks so much.