I'm confused too...
Are you living with your former husband whom you divorced or is he a custodial parent who should be there for your children when you're working? Do you have any idea why he started drinking again? Not that it matters .... if he's drinking, he's drinking. However, if you two are living together or sharing joint custody, you may need to know his motivation to some degree.
I wouldn't want someone like this attempting to care for my kids. Do you have other family members or close friends who are reliable and can care for your children while you are at work?