If your spouse isn't paying child support regularly, is it okay to withhold custody of the child? No.
Is it okay to withhold custody of the child if you believe your child is in danger? No.
Is it ever okay to withhold child custody? No, not in Georgia.
In Georgia, if your ex isn't paying child support, you will need to file for contempt. In the interim, do not try to punish your ex by withholding custody. That's a no-no.
If you believe your child is in danger, call the Department of Children and Family Services or the police but don't take matters into your own hands and withhold custody. What you can do is file an Emergency Motion With The Court for Temporary Custody of your child. Ultimately, the Court will have to decide whether there is a danger to your child that warrants a change of custody. That is not a decision you can make unilaterally.
Keep in mind that if you do make the decision to unilaterally withhold parenting time from your ex, you risk being sanctioned by the Court or, even worse, losing primary physical custody.
It's always been to utilize the procedures the courts have in place for custody changes. If in doubt, reach out to a lawyer for advice on your specific custody issue.