This matter is no joke to assume. It must be verified by either 4 witnesses or the person himself or herself admits.

 

My advice is to check the status of the matter. Was it a onetime mistake and the person is repenting and asking forgiveness from Allah and promising to never do that again? If people admit and they are repenting to God never doing it again, there should be space for reconciliation to save marriage especially if kids are born.

 

If it was an act that is going to continue and no remorse or intention to change, divorce might be an option.

 

Almighty Allah knows best.