It speaks volumes OP that he messaged you images of his new flat. On some level, whether consciously or unconsciously, he still considers you and expects a level of emotional support and validation from you. When you step away from it, it is rather breath taking of him to expect that. What was he wanting? You to say 'oh wow looks great' like some sort of doting mother?
Meanwhile, you are grappling with the reality of your new life and the grief of losing the set-up you expected.
That's not to blame him, but there is an element here that he is probably experiencing that temporary, short-term joy of the 'new' and 'fresh start' because he is not at the 'site' of the break-up, but at some point, he will also have to face the grief and the new reality.
Reality does not stop for anyone.
You are on different timelines and different trajectories now. By choosing to end this relationship, both of you now need to strike out on your own and grapple individually with what that means.
For you, in my opinion, the main goal is to emotionally separate from him by confiding in good friends, doing something small and new for yourself and reminding yourself that one season of life is over and the next one is beginning. He is not part of this new season of life emotionally, even though he will be physically and practically as the father of your children, and that's the best place to concentrate your efforts in my opinion to 'claim yourself back' for want of a better phrase.
Sending you so much love and light OP. Happiness does not come from new flats, but from facing new realities with kindness and courage.