Chin up girl... take a step back, rethink the whole DB philosophy and make sure that you are implementing. I'm not hearing that you're done, and any marriage w/ kids is worth saving. It can be done. Even if your choice is not to save it, self inflicted punishment like you described above is something you have to learn to deal with right now, for your own sanity. I feel ya so much on this one...
I'm still thinking what I was thinking last week. You ask if you can make it three more years and suppose you will "know" at the end of that whether the marriage is worth saving. Think about that... You are NOT done! Get back to the basics of DB'ing. Start doing things right and see if you can't save this marriage! If you are thinking that you'll give it three years for the sake of kid(s) then make it worth your while. If nothing else, if you go back to basics and GAL then you will start feeling better about things in general.
And yeah, WHY in the world would you feel like a failure as a wife and mother? Come on now... get your chin up and start MAKING yourself have a PMA. You didn't fail, he failed you! I really think you ought to quit thinking about divorce and start thinking about giving yourself a boost and doing what you can to save the marriage. Even if the latter fails, you will feel better knowing you have gone above and beyond.
