How can I help my mother deal with a break-up?

My mom called me last night telling me her and my step dad are calling it quits. I guess he had another cell phone we didn't know about. Of course that's a sign of cheating. He done this before and she went back. I try not to butt in to any conflict. But I'm worried for my little sister =( She's having the worse time. I'm 21 and living away from home. How can I help?How can I help my mother deal with a break-up?
I would be there for your little sis, and your mom, but she is a grown woman who is making bad choices obviously. Just help your little sis to not grow up like that, be an example for her. Hopefully your mom has learned from this, and will not try to look for any type of relationship to meet her needs.