Based on your facts, you are the only parent automatically allowed to claim the child as a dependent. You do not need a form 8332.
In any year where you will allow your ex to claim the child, you give your ex a signed form 8332. On your tax return you indicate that the child lived with you, that you do have a custody agreement, and you did give the other parent a form 8332. Turbotax will not claim the child tax credit for you, but will allow you to claim head of household status, EIC, and the dependent care credit (if you meet the other qualifications) because those tax benefits always stay with the parent who had custody more than half the nights of the year and can't be waived, shared or transferred to the other parent.
