Having an extramarital affair is a ground for divorce. So if your spouse had an extramarital affair, that gives you the right to bring a lawsuit for divorce if you so choose.
Now, if you have condoned it or forgiven them for it, then you can’t later, years from now, come back and use it and hold that against them. So it must be uncondoned. In other words, you didn’t know about it and when you found out about it, you took action.