Can I still set aside my divorce for custody purposes if my ex gets remarried?

If custody is your only issue then his remarriage would not preclude you from pursuing your set aside motion.

I am not sure what the basis for setting a divorce aside would be other than fraud. You may be able to modify the custody order, but the divorce is still in effect.

If you qualify for a set aside of a divorce, then you qualify regardless of what the other side is doing. However, if all you disagree with in your divorce is custody, then just file a motion to modify custody, rather than relitigating the entire case.

You cannot set aside your divorce setting aside the divorce would you mean you would be still married to your ex. but you can challenge and change custody provisions for your children if there is a change of circumstances. Your ex getting married would be a change of circumstances. However you must be able to show that changing the custody provisions is in the best interests of the children. If your ex's fiance is a good person (no drugs, alcohol or mental issues) this would be harder not a lesser burden to win.

Most divorces are not set aside, although custody can be charged if there is a sufficient change in circumstances.