I think you need to pray for your spouse, that God will save them, and the marriage.
As for this demon nonsense, if it was that bad, you should have seen it before you got married. Just because someone has a temper, or overspends or whatever, doesn't mean they are demon possessed. Any common mental illness can cause that.
If you are talking adultery, you do have grounds for divorce, but that still doesn't mean the spouse is demon possessed.
God can change any heart, always remember that!