To start with, stop with the "blame" and beating up on yourself.....you have already had a bucketful of blame cr*p from Mr Wonderful, so let that all go out the door.
As for how to let go, and stay that way......gee whiz I wish I had the answer to that, as I'd be a very well off woman.....which I'm not.
Mind you, thinking over Suki's idea has me nodding....I guess taking action to divorce, instructing a lawyer, seeing the papers actually before your eyes, and ordering the filing with the court could help. At the least it would not just be sitting in the mud puddle, crying cause you are wet and dirty.....you would be doing something to get out of the darn puddle, and it would send a message to Mr W in more ways than one.
It seems to me that til you decide how you want your life to be, and commit to that ideal....you will remain caught up in the go away/go back scenario.
But first, get off the stage and stop joining him in that duet of blame agin you.
God bless