I think it's great that you had a nice visit with your family today, sorry it didn't end well. I agree with deleting the voicemails before you listen to them, just adds insult to injury at this point, why put yourself through the agony, right?
Perhaps the reason she brought this up now, other than finally being ready, is because she wants to be sure that you go through with the divorce. It may sound a little strange, but perhaps now that she knows you are not going to stay with him, it's a safe time to tell you why she has so much trouble with him, and with you being with him.
This is the only example I can think of, a woman will rarely tell her girlfriend what she thinks of her boyfriend until she knows they are breaking up... that's when the truth comes out. I hope this makes sense.
As far as where were you? You were doing the best you could with what you had. You can't change the past, but you can definitely work on the present, and it sounds like that is what she wants to do as well. Remember, you did the best you could. And many don't get a second chance, a chance to heal with their families after the fact.
You have a great opportunity here to make amends/work through this with your children, take advantage of it, when you are ready. You have alot on your plate right now, and the best way to get through it is to continue to focus on you, even after finding out what you found out. Sacrificing your recovery for the sake of your daughters by doing things you aren't comfortable with right now, might be too much at once. One day at a time, one thing at a time. Keep taking care of you!