CS-
Ouch, what a week you have had! Big [[[[[[CS]]]]]] for you. Please don't be too hard on yourself for what you did. We are only human and cant be expected to be perfect all the time. You did a great Plan A for 3 weeks, you should be proud of that. If the last 3 weeks didn't have a positive effect on WH, well, then his head is in someplace else besides the fog. A lot of the things he has said to you are classic WS-babble, we have all heard the exact same thing many times before. Don't take any of it too seriously, he is only trying to put all the blame, pain and hurt on you, but you wont accept it, will you.
Maybe its time to take a break from all of this, not a Plan B, but just an emotional vacation from WH for a while. Let him have his pathetic life right now, let him wallow in his own pity, let him have all the time in the world to think about things. Except for issues involving finances or the children, make yourself unavailable to him for a while. Let him come to you (which I have a feeling he will do) and make the effort to initiate contact. It may not be time for Plan B yet, but a little break will give you an opportunity to clear your head, look at things from a different perspective and give you time to recharge your batteries so you can continue to do a good Plan A.
Your in control CS, you are calling all the shots here. Don't let WH and his selfish actions determine how you feel or act. Be proud of how far you have come and how much of a better person you are!
I must admit, threatening to tell his work about him and OW sure took some big cajoles! I'll bet he almost peed his pants when he heard you say that. So, if OW isn't such a big deal, why would he have been so defensive about it? And the line about OW not being the reason for him leaving- WHATEVER!