I can say out in the open that he does not have a drinking problem. In fact, I drink more than him lol. He hardly drinks at home, maybe have one or two beers with me on a Saturday night, but he does meet his friend after work for a few evenings when he is not at mine with me (we don't live together just yet).

He's never aggressive when he drinks or if he doesn't have a drink and he hardly goes out 'partying' like the majority of his friends do his age (he's only 25)

I think the main issue here might be that his perception on how serious the matter is doesn't match mine. Whereas I don't and will never tolerate such behaviour and I don't have a drink of I'm driving myself, he is clearly more relaxed about the subject.