Live the forgiveness. You don't need to forget to forgive; indeed, to do so would be foolish or you'd repeat your errors. Learn from the experience and apply it wisely down the track. But do let go. Don't wear this issue around your neck forever more, bleating about the injustices to others every chance you have. By all means talk things through with someone you trust as a means for righting your perspective and moving on, but don't harbor anger, or harp on about what happened. To do so would be to allow the promise-breaker to keep on breaking your heart. Ultimately, your compassionate empathy in understanding their motivation and in distancing yourself and shoring up your own defenses is the best form of forgiveness possible.