One thing to note is that even though God is all-powerful, there are things He won't/cannot do. All-powerful does not mean the ability to do what is logically impossible. God, for example, cannot create a married bachelor, or a square circle, or a stone so heavy that even He cannot move it. These are logical absurdities. In relation to your case, because God wants to create a world of free-will, He will not simply change your husband's heart in an instant because He cannot do so without manipulating his free-will. Changing someone's heart from one extreme to the other without completely controlling their free-will is simply not possible. If your husband insists on a divorce, God will not force him to stop or change his mind. God can change hearts, yes, but it will take time. He changes our hearts slowly by reaching out with His pure love. It will take some time for your husband to see and understand the love of Christ in you.
If you're worried about black magic, seek out any Christians, pastors, or priests you may know. Ask them to pray with you. There are people within the Church who specialize in exorcism, which involves praying against demons and black magic.
Please read the resources I recommended to you earlier. I will continue to pray for you.
