NEED ADVICE FOR A FRIEND

Basically my best friend has been married to her husband for 2-4 years I believe. They have 2 children. And the husband has been sleeping with and dating another woman behind her back. Telling everyone that this other woman is his wife. He has pretty much moved out and is living with this other woman and her 4 kids. Leaving my friend at home with her 2. He doesn't support them. He doesn't pay for anything and barely sees the kids. When he does see the kids. He picks them up at 8pm and brings them home at around noon the next day, baring in mind the kids go to bed at 8ish. So they pretty much fall asleep in the car he takes them wherever and puts them to bed. And as soon as they're up and ready the next day he takes them home. So he doesn't actually spend any time with the kids.

She wants a divorce but he is saying he will point blank refuse to sign the papers because and I quote "I know that when I've got my head together we will work out" which to me means "when I've finished having my affair or when the woman I'm sleeping with gets bored with me I will come back to you" I hate to see my friend been used as an option. And she needs to know how she can get a divorce asap without his signing.

I hope I've not missed anything else. If I have then just ask and I will ask her :)

Any advice will be appreciated! X