Say to him if he has not got a problem, he needs to go 1 week with out it. Tell him if he loves you just do this one thing for you, and prove you wrong.
Check all the house 1st for alcohol and remove it. Chances are he prob will fail. Or refuse to do it.
Addictions happen to the best of us, good dads, people who are financially stable and good job have addictions, if not worse as they can afford it and get more.