First of all God would never want someone to stay in an abusive relationship. The problem people forget is the equally yoked part. If a person who is a believer is married to a non believer the non believer is not under the same covenant . They will go on living life as they choose . Most people do not understand that if God did not bring the marriage together than people by their own choices bring about a marriage that was never meant to be in the first place .
A woman is to follow her husband as he follows Christ if at some point he is not following Christ than she is in no way suppose to follow him. If he is starting to be abusive than even if that means separating until he gets it right. If it involves sexual abuse than she would have to protect her children. God does not believe in divorce but that is for marriages that he has put together .
A marriage that He puts together will last because they understand that God is the Center of not only their marriage but the center of EVERYTHING . How can a marriage fail when God is in fact the center of it all? . Not just when it is convenient but the center all the time. A marriage built on Godly principals and a Godly man leading there is no way the marriage will fail .
If he is in the Spirit and is being led by The Spirit than he will discern when the marriage is in trouble and take action .
People get so confused about marriage 2 non believers that get married are not under the same rules so to speak they are just 2 lost people trying to make a Covenant work in a way it was never designed and when it fails inevitably than they want to bring God into the picture and say well God does not believe in divorce , it is plain lunacy .
God had nothing to do with the marriage in the first place . People put to much on God and not enough accountability on themselves for placing themselves in positions and situations and circumstances that God had nothing to do with at all to begin with.