Yo yo marriage

I have a 39 year old daughter who has been married for 12 years and has 2 children-8 and 9. The marriage has been tumultuous since the beginning as the man she married is very verbally abusive-never get physical but lives a very negative life filled with how bad he has it (good job, beautiful home, a wife who works a fulltime job and is a wonderful mother?). If you don't agree with him you are the target of his verbal abuse. My daughter has vacillated back and forth about leaving him, has even seen an attorney-only to go right back in to the same situation.I am at my wits end. Help!!!!!!