Hi: I am sorry that your life has taken such a turn. Anyone who has lived with someone else's addiction can identify with what you have written. It is text-book.
The first thing for you to do for you is to find some Al-Anon meetings in your area; or, see what is available on line. It has saved the lives of many, many people. It is anonymous and I have never known that trust to be broken; it is free; it is supportive; and you will gain much if you choose a great sponsor. (do not make this decision too quickly).
Get the book, "The Courage to Change." It is a daily reminder.
For your kids, take them to an Al Anon, Al-Ateen, or Al-a-Tot. If there are none, start one.
Keep the focus on yourself, not what your addict is doing. It is not about the addict. It is about you. "Let Go and Let God."
If you are doing any of the following, stop: picking him up when he falls on the floor; clean up after him if he vomits, etc., worry about him not looking at you-- it doesn't matter; if he is pacing, go sleep in another room or invite him to sleep elsewhere (do not start a fight over this, just take care of yourself. You need to be rested for your kids.
If he gets arrested, do not smooth it all over for him; if he gets in the car high, call the police. Do not let your children get in a car with him. Are you starting to get the idea that this is not about him, any longer.
AS you fail to get ensnared in his drama, he will have the space to get his own help.
Get a copy of the book, "Co-Dependent No More." by Melody Beattie.