You're probably right. Really if you start pushing him about drinking you become the enemy. I'm sure you already know that his first alliance is to alcohol - above everything, including his family, even himself.
When he's not out drinking at some hotel texting some woman, what's he like? I mean day to day when he is "sober". He just pretends like everything is normal? Does he ever speak of getting help at all?
This is really a horrible situation for you and your child to be in and I am so sorry this is happening to you. All you can do is keep moving forward.
Have you heard of the book Codependent no more by Melody Beattie? Lots of good information in there about boundaries and relationships, you might find some information in there that resonates and is helpful.