It sounds like you have been through hell and still going through. By all accounts, it certainly looks like he is in DENIAL or he just doesn't know how to STOP what he is doing. The young girlfriend is also part of his 'fix' right now. It's not unusual for addicts/users to team up like that...neither one has to deal with the guilt when they are with each other.
You've got to put yourself and your kids first or people like this will destroy your soul.
Be Well
and
God Bless