You only have 6 months from date of finding out about adultery to file for divorce on these grounds. He is playing for time to get his ducks in a row.
Now YOU take control. He has had the control. TAKE it back right now.
If the 6 months limit is true for adultery grounds, then file for divorce now. You can always change course later if that's what you want, but file now.
And stop being his 'wife'. He's said he wants it all: his home, with you taking care of everything including your DD, while he spends family money on his new woman. Fuck that! Move his clothes into the spare room, try to get him out into the annexe, and do absolutely nothing for him: no cooking, no cleaning, no ironing, no keeping him up on his insurance, etc Tell him he's on his own since that's clearly what he wants, and he has no business telling you how you feel.
And tell him your DD will not be shown that this is what 'normal' looks like in a relationship. Tell him he has let her down as well, blown up her world, given her a really shitty example of how a husband treats his wife.
I would start letting people know, too, OP, so he can't put his own spin on things, such as pretending you were already separated, it had started after you agreed to separate, etc And tell his mum. Have her come this weekend, but tell her you're taking DD off with you for the weekend away and she can have her tosser of a son back for the weekend. Suggest she help him pack his things and get out.