Though adultery is a very serious sin, even God's word the Bible says that we should not commit adultery and in the mosaic law anyone who committed adultery was stone to dead but when Jesus came to the earth he said that adultery is a serious sin too and it is the only ground for divorce, but if the couple decided to forgive one another if at all one of them committed adultery they can do that.
My opinion is best on what the Bible says, adultery can be forgiven if the person committed it shows a remorseful attitude and if it was not intentionally, because something can leads to it.so I will say that it is possible to forgive though it is painful.
Why I said so is that the Bible says that we do not know how many times that we sin against God but he forgive us and if we want God to forgive us of our sin we must forgive one another who sin against us.
The person that is cheated should repent and seek for the forgiveness instead of trying to start another relationship because it might not work for him/her
Thanks for reading my opinion @steenit-family