Irretrievably Broken, aka No Fault Divorce
This means that you have grown apart or there is some personality conflict that cannot be resolved. You are stating that there is no hope for your marriage; therefore, you wish to terminate the legal relationship you have with your spouse. If the parties continue to have sexual relations, some judges will interpret this to mean that the marriage is not irretrievably broken and may dismiss the case.

Adultery
A person commits adultery when s/he has sexual intercourse with another, other than their spouse. It’s interesting to note that if your spouse had an affair months or years ago and you forgave them and welcomed them back into the marital bed, then adultery is most likely not a proper ground for divorce. 

Cruel Treatment
Cruel treatment is an infliction of bodily or mental pain that’s enough that reasonably justifies an apprehension of danger to life, limb, or health. The most common use of cruel treatment will be in situations where domestic abuse has occurred in the marriage.

Desertion
Desertion is the voluntary separation of either spouse from the other or the voluntary refusal to renew a suspended cohabitation without justification either in the consent or the wrongful conduct of the other spouse. Georgia law requires that the desertion occur for a minimum of one year.

There are other grounds that are less common but allowable under Georgia law.