In regard to him turning his back on your kids I would view it as the biggest blessing ever bestowed upon your family. Kids never deserve to live in a house of addiction, NEVER.
They may not fully understand all the circumstances today, but one day they will be so very thankful that were not raised in a house of pain, and turmoil.
You and your kids deserve normalcy, peace, love, comfort, security, that is NOT something he could offer or provide. Raise the bar for yourself, and your family.
In gentleness I say, playing the "how could he leave my kids" card is YOUR transferred pain. Dig down a little deeper, get brutally honest with yourself, this is not about him abandoning your kids, for God's sake, he was never really there......... Addicts are not good role models for children. period.