My girlfriend has a crazy Ex and its killing me?

A girl I used to date back in the day..."the one who got away". Has come back in my life after almost 10 years. In the years that have past she married a scumbag, pathological liar, who cheated on her most of their marriage. Which is stupid because she is WAY out of his league...and he should have considered himself lucky to have her as a wife. When I showed up in her life...she realized that she should have done much better than him. She asked him about the infidelity and he admitted it out of cockyness because he had her so abused he, thought she wouldnt do anything. She is now divorcing him....he is freaking out. He is making her like a living hell. Threatening legal action with the kids, making up stories to make her look bad to fellow parents at the school...just plain old manipulation of all the people connected to her. Its is ruining her life. Basicaly he said, if you are going to divorce me, I am going to make sure your life is ruined. Now to the question...I love this girl. She is all I have EVER wanted. My hatred for him is keeping me up at night...he texts her and calls her names like fatty, and cottage cheese thighs (when she isnt fat) but he is just that type of guy. I want to protect her! I cant have somebody talk to my girlfriend like that...or my future wife...it doesnt matter if they were married, or they have kids. I dont know what to do. The stress of how easy it is for this guy to be a scumbag makes me SICK. And the good people get run over. I know there are legal steps that can be taken, but they cost money....which we dont have. I basically need help to separate myself from this fight so I can focus on work...but still love and protect her. This guy is the WORST person anybody could have in their life...why does he have to be in hers...the love of my life. Please somebody tell me how I can deal with this stress.