Oh Ophelia, my love. I've read your thread and what comes across loud and clear is your strong sense of what is right, and his blatant disregard for it. While I wholeheartedly applaud your determination to do the right thing and not lower yourself to his appallingly low levels of decency, I think you're misguidedly holding back because you don't want to upset or anger him.
I think we're all rooting for you to stand your ground here. He thinks he knows you and knows that he can dictate what happens and when. He, through his actions of late, has clearly shown he has no morals or any sense of remorse about what he's put you through. While I don't think you need to turn this into an out and out war, I think you're more than entitled to fight back. This can be by telling people what he did, or by standing up to him in any way you can.
If you stay quiet, he will continue to rewrite history and tell the 'we were rocky, I'd been unhappy for a long time' story which we all know isn't true. If he's so happy to move on so quickly, lock, stock and barrel, then he should deal with the consequences, which is that everyone knows what the story is. Noone will laugh, noone will judge you and you will find the most amazing support is out there. He, and his cheap, nasty replacement can deal with the fall out as it's no less than they deserve, but please my love, for your sake, don't feel afraid to be truthful. He lost the right to your protection (because, this is what you're doing) the moment he betrayed you.
You deserve so much more. He deserves nothing but your contempt, but that will come.
You are doing so well, even if it doesn't feel like it. Be strong, and take all the offers of support that are out there.