As long as it doesn't affect his work/the firm,that's his business. At least you know ahead of time what **can happen** when 'over drinking' happens. I swear, I'm such a better business partner/boss/friend now that I know the addicted mindset feeling/signs. It's pretty amazing what I noticed about the people around me and life in general after being sober a while and getting myself sorted. There's a lot of heavy drinkers that think they're 'normal'. Not my business,unless asked or it affects me,though.
Edit: Congrats on the new firm!