How to help a friend in crisis

My friend just came over to my house because she is having a total melt down. This morning, her husbands phone beeped while she was getting ready for work and she grabbed it so it wouldn't wake him up because he doesn't work. It was a Hangouts message from someone who had posted an advertisement on Craigslist for sex. She saw it and read through previous conversations he had had with LOTS of other women. They exchanged photos, talked about prices for sexual acts, and planned meetings. 
My friend is so hurt. They've only been married for 5 months and she was so excited to spend their first Christmas together. 
She says she plans on divorcing him, but she's said that in the past when she found him cheating, when he hit her, and when they got into a fight that resulted in him trying to commit suicide in my driveway. 
What can I do to help? She hasn't confronted him yet and he's been known to get violent when confronted. She just left my house. 
I don't know how to help. I've never been in a situation like this before. Advice?