My suggestion CO Dad, after reading your response is this:
You are doing good. A lot of men I know would just keep looking past these kinds of issues. The most troubling thing to them would be that they had to get up in the night, not that the wife was passed out on the couch. Keep up the good work, you are a good Dad.
Remember, you mention getting custody. Start acting like it is just you. When an incident like this happens, act as though she is not there. You need to be able to go comfort your son without your wives help. If you get full custody or even half time one day, you will need to be able to do this.
Then come back downstairs, grab your cell phone and snap a picture of her passed out. There is no comparison between a letter you write her and showing her how it really was.
This sounds tough but parenting is tough. There is no easy way to say that your child needs to come first. As soon as I realized that this was my role in life, it made standing up to my husband, and doing the right thing for the kids, so much easier......
Thinking of you Dad.
4MyBoys