GH, if and when it does appear that the OM is gone, you may want to suggest that the two of you attend one of those weekend marriage retreats. Those things work like intensive counseling and can sometimes produce dramatic results.
Even if she still hasn't completely broken it off with the OM, those things can still sometimes work.
The LORD is near to all who call on him, to all who call on him in truth." (Psalm 145:18)