I'm glad you are going to Al Anon and I hope you have a really supportive group.
It is impossibly hard, but you know you are right. Being right isn't always a happy thing.
because I have to stick to my boundaries, and I’m responsible for the kids’ well-being
Even if you wouldn't do this for yourself (I hope you would) this is kind of the bottom line. He is also responsible to provide a safe environment for the kids and for everyone really. If you can't depend on the adults in the household to behave responsibly, who can you count on?
You are actually also setting a great example by showing them that you don't just stay "loyal" and stay with someone when their behaviour has become intolerable. That's a big deal.
Now is a great time to focus on yourself and what you want.