VB - well done. I think you've coped with a very hard day very well.
I think the word "breakdown" is used too easily by some people. It's like people have a mild cold and they make it into flu. Because of my work, I deal with people who have real breakdowns frequently. I doubt OW is having a breakdown, she's just overwhelmed with grief. That's normal and natural. I also think that your ex is incapable of supporting another person, he doesn't want the responsibility, he can't "give" to others; other than empty words, meaningless gestures - I'm with you on the flowers btw, I'd rather be given something to grow than something already dying too - it's so easy to buy things, to give something, but this man is incapable of giving support of being anyone's "rock".
So I wonder if OW grieving and needing him for support has blown this relationship apart. She's seeing him as he is, someone who needs all the attention and ego-massaging; and he's seeing her, not as an exciting bit of fun, but as a real woman with real emotional needs.
He can't give you or her what you both deserve. So he then makes it about himself, and has "an episode". Now, I've dealt with people who have "episodes" often after they've been sectioned. He, like the breakdown, doesn't have a real "episode". It's just a tool he uses to get your sympathy, get your attention and get you back under his control.
He still wants to control things with you. "We'll talk more on Thursday". This shows you that what you've said hasn't registered yet, or if it has, he's refusing to face it. So you just have to remain calm and resolute and repeat what you've said. No, there's no going back. It's over. You don't have to justify it, or give him support. Just calmly repeat what you want. And like a small kid, he'll kick off, he'll have another "episode" or another "breakdown" - i.e. the equivalent of a toddler screaming in the supermarket, laying down and banging the floor. Treat him the same - calmly walk over him, and grab what you need off the shelf.
You're doing well - getting on with other stuff, rebuilding a life on which you can start having good times away from him. It takes guts, I admire you.