I would leave well enough alone for now. Don't send him the note because he will look at it as manipulation and/or not read but the first line or two. You'll get the opportunity to tell him how you feel at a later time.
Keep the focus on you and your children. You didn't break him, therefore you can't fix him. His problems are his to own and no matter how many times you apologize, it will go in one ear and out the other right now. He's not ready to really focus on and hear what you are saying.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.
