WOW!
what a ride.
I totally understand and have been in a very similar place before. No it is never easy. There is never a "right" time for a divorce that will make it easier. It is a very hard thing to do.
People like you and I seem to over think all these decisions. Most people, and certainly self centered narcissistic alcoholics, would never agonize over these decisions. They would see what is best for them and them alone. Then make it happen.
When you can, separate the emotion from all the logic. Your love and caring for another person can easily defy all logic. Your concern for her well being is part of who you are. But it should not define you.
What defines you is more of how you act as a father and a leader.
After you think about all that is going on around you, your path will soon be clear. Regardless, it won't be easy. But you will choose it and you will be better off for it. And most importantly, your son will be better off. At the end of the day, that is what it is really all about.
be strong. And find a little peace right now. You need it.