There is always an ultimatum with an addict...for me it was "you use crack, you are out on the streets" and I followed through.
If you said you would divorce him if he didn't go to appt. then you have to follow through. You have to stick to the boundaries that you created yourself. If we don't do that, then we being a true codie.
I would remind him of your boundaries, your requirements "before" he messes up, so it's still up to him.
Hope it works out for both of you...
Hugs, SM