That’s more of a AA truthism than anything grounded on evidence.
theatlantic.com/magazine/archive/2015/04/the-irrationality-of-alcoholics-anonymous/386255/#disqus_thread
There is no reason to think of the problem as “you’re either an alcoholic or you’re not” or “you’re either a porn addict or you’re not.” The OP’s husband might need nothing more than confession and repentance and not AA treatment or sexaholics anonymous, which are really not treatment programs based on any evidence and might do more harm than good.
I’m not saying he’s an alcoholic. I have no idea if he is or isn’t.
I am saying that alcoholic behavior varies wildly, but that the main point is this: she’s bothered by it. She can’t make him do anything, but she can work on her own reactions to his behavior. She can sit around being wounded and hurt and angry and lashing out, or she can say “I’m hurt and angry, but I want to respond well in this situation and not just on my (understandable) feelings, so how can I go about doing that?” Which is what Al-Anon is all about.
Her asking him to go to AA or a SA meeting will be pointless, even self-defeating, which is why I didn’t suggest that. If he decides he has a problem, he can choose to go; he’s an adult.
So’s she, so if she’d like to find one way to learn better reactions and to accept without necessarily acting immediately upon her (again, understandable) feelings, Al-Anon might be a very good fit.
ETA: and much of the above is true also of porn use, too. Occasional use doesn’t mean someone’s an addict, though of course, in Catholic theology, a drink or two, barring unusual circumstances, isn’t itself a sin, while deliberately searching for and looking at porn is. With porn, though, the same thing about reactions holds true: whether or not he’s addicted, she can’t control whether he’ll use it; she can only control how she reacts to his usage of it. (Naturally, she shouldn’t be buying him gift cards to his favorite sites, either, but that goes without saying.)