OP, you’ve got lots of virtual handholds reaching out to you.
With regards to your internal dialogue, try to speak to yourself as you would to your closest friend. Would you let her continue asking “what did I do wrong to deserve this?” No, you would be there to gently guide her and let her know that this wasn’t her fault - so try to be as kind to yourself.
I agree with a pp - it might be worth an appointment with GP, even if it’s by phone, to maybe think about a mild sleeping pill. Just to see you through the near-term - sleep is really important. Tablets are not something I suggest willy nilly, but you won’t be functioning properly if you are exhausted.
And don’t beat yourself up for “grieving” about what has happened. I know you’re trying to be strong for your dc, but there is nothing wrong with the emotions being thrown at you.
I really hope that you’re able to go to your sister’s for Christmas. Take your comfy pj’s, fluffy socks, shit loads of chocolate and wine. Have fun cooking the xmas dinner together, watching the kids unwrap presents, maybe stomp out in wellies for a brisk cold walk. And then, when the kids have gone to bed, spend time with your sister where you can just be you.
You probably don’t fully comprehend it now, but your strength and care for your kids really shows in your posts. You really have got this. But let yourself take strength from family and friends that you trust and feel comfortable with. And don’t ever feel bad about saying you might need some help (in whatever form - family/friends/GP etc) as that’s the sign of a really strong person.
And keep writing! Don’t ever let that be taken away from you.