LWB, I don't believe that in the past few months you didn't tell him, in one way or another, that you wanted him or the M. You have said that. He's just remembering what he wants to remember. You've stood strong for quite awhile, and that's what he is seeing. Just the fact that you said you would wait for him to decide proves that. Good Lord, you put up with all the contact with OW and he expects you to be all lovey-duvey?
I think if he saw you as the root of his problems he would have been gone a long while ago. He thought it was going to be his decision, that you were waiting for him to decide. Now that you've forced the issue, I'm sure he's shocked.
He just won't let go of the problems. The past is the past. He's holding onto to them for justification for the A. If he let's them go, then where is he? I think Mark is right ... he is one insecure man right now.