Sorry that you had to run the family taxi since he was drinking.
I'm glad your son can trust you to be there.
I was married for 14 years to my AH. We have a child together and he was stepdad to my other two children.
Here are some things that I have tried to remember when dealing with AXH's:
Don't ask questions that you already know the answer to, like: "have you been drinking?"
Don't expect AXH's to keep promises to their children, alcohol will interfere.
Don't expect to force AXH's into active parenting during or after the divorce. The active relationship they will pursue is with alcohol.
The upside: your children will know that they can count on you to be there and take care of them.
Vent away. We know how frustrating this can be.
(((hugs)))
{edited to add: AXH (alcoholic ex husband) can also mean AXW (alcoholic ex wives)}