I'm so sorry. You are clearly so very heartbroken.
It would seem the prescription narcotics "awakened the beast." It is well known that recovering addicts should avoid all mood-altering substances, as they will trigger the obsession and compulsion mechanisms in the addict brain. Recovering addicts who have surgery have to have intense support afterward to avoid full-blown active addiction as a result of narcotics in surgery and after-care.
He is in the cyclone of addiction right now, and he has no idea what he is doing. His abandonment of you is part of his mental chaos.
He knows where help is and he knows it works. But his addiction has become a lot more complicated with the benzos, as they are very hard to get off, and extremely dangerous to stop cold turkey. He will need medically supervised detox and intense rehab, probably, followed by a return to a 12 step program worked daily and rigorously, multiple weekly meetings for a long time. He is as lost at sea right now as a man can be.
So: that leaves you and your life, and your responsibility to yourself, and your responsibility to the other relationships in your life, for he is off on a long voyage right now, and there is no telling whether he will return nor in what condition. You can pace back and forth on a lonely balcony. Or you can straighten your shoulders and do your work: recovery and life.
The rest of his story and yours will unfold, beyond your control, your timing, your design.
Continue your meetings, continue counseling. Stay on track. More will unfold.