Alcohol is a mood-altering psychoactive drug, and once a person had developed an addictive personality, there is a high likelihood of cross-addiction - that is, switching the attachment from the DOC to another mood-altering substance. That is why most rehab facilities frown on an addict imbibing in any psychoactive substance. Moreover, many addicts find that indulging in another substance - like alcohol or weed - weakens their resistance to their DOC. When they're high on weed or drunk, they are that much more likely to think that "just one more time" with their DOC is a good idea.
Addiction is tough to beat under any circumstance; opiate addiction, though, is one of the toughest. The relapse rates are highest for alcohol and opiates, and the long-term recovery rate for opiate addiction is in the 10% range. Your husband might think he's special - that he's not like all these other addicts, that he's too smart, accomplished, mature, whatever, and that therefore, he doesn't have to do what all these other addicts do. He can drink alcohol and be fine. He can just get his Vivitrol shot and not deal with all the "recovery community," NA stuff. FYI, that is a recipe for disaster. He will most likely soon find out that he's not so special. I can't tell you how many addicts want to carve themselves out from the pack, thinking that they are unique - they are convinced that they aren't the "hard core" addict and therefore don't need to follow the approach that the experts tell them is necessary. This kind of thinking is the NORM among addicts - at first. And then, after multiple relapses, they might realize that they are no different from any other addict. Addiction is addiction, and it is the same no matter your intelligence level, socioeconomic status, age, race, gender, the car you drive, etc., etc. It doesn't discriminate.