If the opposing party in the case has lied in court about having an a marital affair how can that be proved in court or out of court in a custody case?
It is also very rare for an affair to have any effect at all on custody. One's right to parent is not related to nor contingent upon fidelity to one's romantic partner.
If the opposing party in the case has lied in court about having an a marital affair how can that be proved in court or out of court in a custody case?
The sexual misadventures of one or both partners only matters in a few US states these days.
Fortunately for you, Georgia is among that small minority of states where adultery can impact the outcome of a divorce.
I suggest you start by discussing what you know with your divorce attorney, or an attorney you'll need to hire to assist you in prosecuting this matter.
If the other party did commit adultery during the marriage, if proven, it'll only impact alimony in Georgia.
Adultery will not impact custody or visitation with the issue of the soon to be dissolved (or dissolved) marriage.