The only real progress many of us ever make happens AFTER we figure out that we don't need to end one thing, end a behavior, end a mindset, end an idea, to start a new one. You can move on, just become a job having, car driving, independent mother of two beautiful girls that is starting out in life with the determination to make things as great as they possibly can. That says NOTHING about him or what he says/does today, tomorrow or 5 years from now.
Emily, each new phone call from him or cassie, or each new post on myspace does NOT mean a new decision has to be made by you. Other people's words or actions do NOT REQUIRE a response from you. You can simply not make them part of your life's direction. You can simply listen and then move on, taking NO action. That's what detachment is about in some ways.
I know Amy keeps saying you are not strong enough for certain things, but I think you are SMART enough to figure this concept out. You DO NOT HAVE TO ACCEPT that anything is over to accept your right to be happy and take action towards that goal. You can be happy, make a great life for you and your girls without doing a damn thing in regard to your marriage. There are PLENTY of things to do that don't involve a R, new or old, and THOSE are the things you do today, tomorrow and as long as you need to.