The more pragmatic may even throw in a "Fool me once, shame on you; fool me twice, shame on me."
Thanks to Dr. Brown we know shame isn't helping anyone change their behavior; guilt is a much better indicator.
So what if the one you want to forgive keeps messing up?
What if you keep messing up?
Do you even believe in the usefulness of forgiveness?
I'm at the stage right now where I'm trying to take it one day at a time. I'll try and stay away from people who tick me off repeatedly. I'll try and reflect on why things may have gone wrong and how I can change my part in it. I've tried meditating and visualizing my stuff float away on a river, releasing it to the wild. I like talking things over with friends, really letting it out when I'm annoyed.
We're all work in progress.
What are you doing, and is it working?