That is a great question and one I have often wondered so many times over the years. I am in year 7 of tolerance (finally following through w/ divorce filing "for good"); my mom took 38 years. I wish I would have had your thought process and followed through the first time! Although, then I wouln't have my little sweeties and I would do it all again knowing what the stakes would be.
Like Suki said, it's a personal decision. And, I completely agree, when you are DONE you're DONE! I have now reached zero tolerance and in doing so hope that I am teaching my children that it is NOT ok to be mis-treated by people for any reason.