OP.
Just keep this in mind.
The way things are at the moment will not last.
Right now, you are at the absolute lowest point, in utter shock, and going through the agony of seeing the person you thought was YOURS and in YOUR CAMP suddenly turn into a stranger who is very much in someone else's camp.
He meanwhile is on cloud 9.
It will not stay like this. Probably not even for a month. Even if he stays with her, things won't be like this. The conversation you just had does not set out the way things will be and the 'feel' of the future. None of this is reality - not for you, not for him. It is all going to change rapidly, and keep changing.
Even if they stay together, reality will bite.
It's very likely they won't stay together.
He may beg to come back.
They may be over in a month and he'll be left wondering what the hell happened there, and is that really what they call a mid-life crisis?
They may stay together, and after the usual ups and downs burn with shame at the utterly awful, teenage way they got together and showed themselves to be such a pair of superficial, deceitful little cheats.
The thing to focus on right now is - have an eye to YOUR future - and act accordingly. All this stuff at the moment which seems so agonising - such as his saying he'll be having the kids 50/50 - none of it is worth the slightest attention as of yet. So, don't go racing in to try and tackle it in your agony, and end up doing stuff, saying stuff, that you'll regret. Icy cool, icy calm, just head down and sort the immediate stuff with as little reference to him as possible. You'll be glad, because there'll be a day sometime very soon where he'll be the one upset, teary and sweating in front of you - and you'll be the one simply not caring that he's hurting.
The bottom line is, if he's working full time and you don't want him having them 50/50, you can tell him to take it to court. But that's for the future. Right now, ignore everything he says, keep focused on what YOU want. Fix money, get him out of the house, and if he starts squeaking that it's his house, coolly inform him that it isn't.
And next time he uses the word respect, perhaps tell him that it sounds kind of ridiculous now when applied to him or her, so perhaps best not to try and pretend to be decent people - there really isn't any need. Cool, calm, dismissive.
And tell everyone. Everyone. His family, people you know it will get back to at work. Yes, they will hate that.