As another who has been burned by a loved one using cocaine (I lost a 14 year marriage), I echo the advice to RUN and don't look back.
Coke is nothing to F around with. It's a horrible, horrible drug. Like the above poster said - if you let him back, you and your son will be collateral damage and will experience a living hell.
Forget the 30 days. He needs to be gone for good as of NOW.