Have you gone to Al-Anon? (The part of A.A. that is for the family)? People there will be able to give you a lot of helpful answers.
Also, excessive alcohol would reverse the effect from Viagra. So I suggest no alcohol for a week and then take the Viagra (with no alcohol involved) to see if he gets a better erection.
Well I use to drink alcohol a lot in my younger days, I'm now 33 years, and now too much alcohol would definitely slow down my erections. So alcohol could definitely be playing a part in your sex life.
However, we won't know if that's the only issue unless your husband stops drinking alcohol for at least a week to see if that gives him better erections.
If after a week and still no erections, he needs to visit a doctor and determine if everything is normal or some underlying medical condition.