George Costanza
A Friendly Liberal
It's up to the individuals and the relationship. For some people it's a real dealbreaker, for others it's salvageable. I can't imagine it ever being painless though, and for me at least trust would be very hard to re-establish. In general I'd say if you're going to give your word, keep it. Or don't give it at all.
Trust can be reestablished. But getting rid of the bitterness is another matter.
Honestly, I don't even know that trust can be built back up again. There may always be that nagging "voice in the back of one's mind"....
Oh it can be. It's called a short leash. A VERY, VERY short leash.