Even Jesus told us not to forgive all things while at the same time condemning the religious leaders in the strongest terms. That should give us a hint somewhere about there. Do you remember what Jesus said was the reason for divorce acceptable to God? Adultery and fornication!
Matthew 5:32: but I say unto you, that every one that putteth away his wife, saving for the cause of fornication, maketh her an adulteress: and whosoever shall marry her when she is put away committeth adultery.
If then for the sake of the sin of fornication and adultery - divorce is permitted, this means that the wronged partner does not have to forgive that person for if they had to forgive they couldn't divorce said person.
In Luke 17:3, we are told that Christians must repent if they commit serious sins against others that may be forgiven. If they do not repent, obviously the sin does not have to be forgiven.
Also consider this:
Matt 18:15 And if thy brother sin against thee, go, show him his fault between thee and him alone: if he hear thee, thou hast gained thy brother. 16 But if he hear thee not, take with thee one or two more, that at the mouth of two witnesses or three every word may be established. 17 And if he refuse to hear them, tell it unto the church: and if he refuse to hear the church also, let him be unto thee as the Gentile and the publican.
As you might realize, the question of forgiveness of sin is more complex than many think. In fact, if you forgive or not does not affect God's treatment of the sinner, it only affects your own peace of mind and God's treatment of yourself. If you look at Paul in his epistles and his discussion about Alexander, I think it is, you will see that not all things are forgotten.
It comes down to this, not all relationships may be restored to previous positions. If a person behaves the rabid dog, you would be a fool to go and get bitten repeatedly by such a rapid dog. If the dog only bit you because you trespassed, and since has become friendly, perhaps prior or better relationships may be wrought .
As it says, '
deliver us from evil', and the ones who are like satan must not be forgiven. But, that does not mean you carry around in your heart a burning hate of them. It means that you let God be the avenger and rely on him to correct things. Then you can concentrate on doing good.