How can I reconcile my parents?

I'm 21 and away at college. My parents have been fighting a lot since before I was born. My father is extremely verbally and emotionally abusive, and he used to hit my mom. Two years ago, we found out he was cheating on my mom, but she forgave him if she saw improvements. Well, he's become abusive once again, and doesn't appreciate my mom for being such a hard worker. Instead, he calls her a "mule" because she has to work two jobs now that he's been out of a job for 6 months (he's selfish and picky and is fine with the fact that my mom is tired all the time). He spends her savings money. Over the course of a year, he spent over $5,000 on that useless waste-of-breath he was with. My mom says she's sick of his antics and immaturity so she told him to leave, and now she's considering a divorce. I have a 16-year-old brother who's in his own self-centered world, so I feel like I'm the only one who can help save their marriage. What can I do to help? Can I do anything at all? My dad refuses to see a marriage counselor, and is very hardheaded.