You do have permission. But you have to give it to yourself. You no doubt feel a ton of resentment towards the OW. But she just sees the same great guy you do. By forgiving OW, you , yes you, will feel liberated. It will be very hard to do if she is still in the picture. Forgetting can't be done. Forgivness can be done. As Jesus said, "forgive them Father, for they know not what they do." http://www.michaeljohnsonphd.com/10_steps_to_forgiveness.htm
I felt the same thing for MIL for quite some time. Let it go and man what a relief. She has turned into one of my biggest supporters.
