Infidelity is unforgivable especially if you are married and have vowed in the eyes of the law to be with someone. It is also destroy a marriage or relationship.
Can you forgive them and give them another chance . Because of the welfare of your children if you already have and you do not want to destroy your family. Or you want to separate because you're hurt..
To me that is the most unforgivable thing in a relationship because it destroys the foundation that the whole relationship is built upon. And when that happens there is no way that a person will be able to come out fully trusting their partner again.