Hi Shans,
I am sorry for what brought you here to us but know you will get a lot of support here.
My suggestion:
As harad as it may be....
Focus on YOU
The kids
being Happy
Forget him, if he doesn't want to be in your life or the kids, it is probably a good thing. If he is in active addiction, would you really want that around your children? I know I wouldn't.
Please also understand, this has NOTHING to do with you. This is all HIM, he is the one who is an addict and chose that life for his family. This is not your fault, you are not making him drink or do drugs.
I hope someday he will wake up and make amends to you and the children.
Blessings,