As far as the potential effect of divorce on your son, it isn't just a matter of mom and dad being unhappy with each other--she is likely to become increasingly unreliable and "checked out" over time. She is also abusive and angry much of the time, and all of that DOES affect him--very directly. Nothing needs to be decided immediately, but don't take leaving off the table. And don't wait until it becomes utterly unbearable for another second, either. By then a lot of damage will have been done.
I'm glad you've decided not to drink around her. I don't know that it will set any kind of "example" she will follow, but it will be one less way of enabling or making it easier for her to drink.
And I have to comment on the "false allegations" articles. In my experience false allegations of abuse are very rare. They do happen, but not nearly with the frequency some of these articles suggest. There are MANY TIMES MORE situations where abuse is not reported, recanted (due to intimidation and other factors), or covered up by the victim and allies of the abuser. As in your situation, false allegations are more likely to be made by the abuser than by someone trying to get some kind of "advantage" in divorce/custody proceedings (which is usually what those articles try to suggest is common). The reason I mention it is that abusive men often point to those articles and many jurors (as well as family and friends of the victim) will disbelieve victims (often because the abuser is very charming and seemingly wonderful to everyone else) and assume she is making false allegations. Just wanted to set the record straight. I have seen a handful of cases out of the thousands in my career where I felt that someone was manipulating the system to her advantage. It looks like the article you linked to has more credibility than most, because it makes clear that false allegations are usually made by someone who is otherwise abusive. I think strictly tactical false allegations (where there is no history and it's just to gain an advantage in divorce/custody battles) are extremely rare.