Depending on the severity, I don't forgive, I'm a door closer. Once someone with purpose and malice betrays me, I close the door, and never look back. By the same token, I don't hold grudges. Some might claim that in essence I am holding a grudge, but as far as I'm concerned, "What's done is done" and I can easily move on.
I've been told it's a character flaw...perhaps they are right.