Hello Lioness Nebula, people can have a tendency to ignore counselling and/or stop taking their medication and replace it with self medicating using alcohol, this can lead onto many other self diagnoses which could worsen his condition and increase his frequency of drinking.
You can't be sure how much he does drink as he could be drinking when you can't see him and become a cupboard drinker, like I was, hiding the grog in places where you wouldn't look, but appearing to only have one or two drinks while you're with him.
As he is ex-defence the current problems around the world could be affecting him, as it is for most of us, but does not want to discuss his feelings with anybody and instead self medicate.
To treat his own depression using alcohol to try and numb his feelings may temporarily work for him, but long term, it's not a solution, as I found out myself, but trying to convince him isn't going to be easy.
A person can only stop when they decide they want to, however you may want to address this is by contacting your doctor and having a chat with them because you have to look after yourself.
Please ask any question you like.