The issue of abuse, whether physical or emotional, is no doubt a difficult pastoral issue. If the abusive spouse is a non-believer, then the case to be made for abandonment would be more directly relevant as such would constitute a Biblical grounds for the divorce. In the case of a believing spouse though it would seem to be much more complex. I'm inclined to agree with the previous poster regarding separation as opposed to divorce.
An abuser is ipso facto an unbeliever.
I don't understand why if the husband is a believer or not would be an issue. Our duty to God should not change based on our environment. Of course, this comes from my view that abuse is not a form of abandonment. That reeks of pop psychology, IMHO (got a useless degree in that field) :)