You are not responsibile for his recovery, you are not responsibile for his behavior, you are not responsibile for his emotional IQ and you are not responsibile for how he feels if he cannot continue to be impulsive and no longer buy everything he wants to for his children.
He is a child in a mans body, he is an irresponsible parent. Accept it.
You need to let go, for you, not him. Expect nothing from him and you will not be disappointed.
Unfortunately parents play favorites, it is wrong, but, this also is out of your control. All you can do is try and keep a sense of balance within your home, be fair, love them equally and don't let his nonsense interfer with your peace and well being.
I know this is a difficult situation, and, I am sorry that your children are being exposed to his lack of parenting skills.