Hi op I just want to say you will be okay in time. Look nothing can compare to shiny new attention from someone new to a weak ol fool. It’s no reflection on you, all him. She’s a bit irrelevant as she will have been fed a load of lies and might have boundary/self esteem issues (not an excuse) it’s not about you, they literally all say what he’s said. You could be the most beautiful attentive fascinating fucking person in the world and this could still happen. Happens to royalty, supermodels and pop singers.
All you can do is know from posters here who have been through exactly the same that you will be ok. Not tomorrow or next week but keep going, you are grieving a future, not really him but a future and when the worst of the grief subsided you’ll realise that the future came from you.
If you can, tell him to leave to live at hers. You can even be stupidly nice about it and say I’m glad you found happiness and good luck, and say live with her (which he should agree to since you are so awful! Ha)
With work, if you’re feeling too ill to do your job don’t go and see your mum? If you can, only you know if that’s doable.
Eat little - smoothies, soup, crisps. I know you’ll have no appetite but if you don’t eat you’ll feel more overwhelmed by your emotions and won’t sleep either. Keep hydrated and lay off caffeine a bit. Fresh air is good and when you get out for fresh air decide that it is a ‘mental break’ from thinking about it all, even if it’s 10-20 mins, this is important as your mind needs a break.
There is a good description I read years ago that helped me during similar circumstances- it’s the ball theory of grief. Will link in next post as sure going strange