I don’t mean to be harsh but ……
You have told him you can’t marry him but you haven’t told him the relationship is over or made plans to separate your lives. And you haven’t actually cancelled the wedding or had somebody else do it for you.
You are still fixated on the details and ignoring the bigger picture that he is nowhere good enough for you as a partner or father to your two little girls.
You are arguing about him not admitting he’s a deceitful, lying, gas-lighting betrayer and I have a feeling that if he did admit his latest of a long string of cheating, and then apologise, you would then still marry him.
Is that what you are holding out for OP? An empty apology and a flimsy promise that means absolutely nothing?
What about next time he does it? (which is likely to be as soon as he returns from the holiday)
He knows you so well. You told him you can’t marry him but he doesn’t take your words seriously. He argues a bit, gaslights you, ignores you, and puts you down then carries on as normal, knowing you said those words in a fit of pique but you’ll get over it.
You have given him free rein to act like a single man whilst you still serve him and run around after him. Business as normal in your household then.
He won’t cancel the wedding and he won’t move out. He is ignoring your feelings and words yet again. He’s moved on from your argument already.
Telling him and your one friend that you can’t marry him isn’t going to cut it OP.
It’s not going to make things any better for you and the girls in the future.
He isn’t going to improve your lives or enhance them for you. He’s a user.
He will diminish you even more, -wear you all down, and you will be stuck. If you ask him to leave, he will laugh in your face and say he isn’t going anywhere.
I strongly suspect that you won’t leave either because you won’t want to disrupt the girls and you really like living in that house.
I understand how this emotional turmoil drains your energy completely and leaves you feeling helpless because you don’t know what to do for the best so you just leave everything floating and make no decisions.
OP, if you really do want the relationship to be over you must ….
Be really clear in your own head that that’s what you want.
Tell your family and friends that the wedding and relationship are finally over.
Cancel the wedding service and wedding catering at the holiday hotel.
Change your flights and hotel for the three of you. Tell your family and friends to do the same.
Also tell his parents that it’s over.
Return your dress if you can.
Make plans to leave him.
I wish you the best whatever happens, but please don’t marry him.