Oh my goodness this all sounds so familiar, it took me a long time to learn to talk about him without bitterness. I fact for the kids sake I just never mentioned him at all. But then I realised how awful it was for my son. He wanted to be able to talk about him, good and bad but was afraid of hurting me. My daughter is her father's daughter through and to ignore it I think resulted in her hiding herself away.
He was an amazing man with the kids when they were babies, and an amazing partner for 8 years we lived in a bubble a rose tinted bubble just us and our. Kids then the last 2 years were horrific and a sht show and he was unbearable.

It's been 8 nearly 9 years and now I try and mention their dad in positive ways, especially if they display his positive traits . And reassure them it's fine to say nice things about him... Or horrible things. Their feelings are as valid as mine. Probably the hardest thing I have had to teach myself.

Oh my grieving started spontaneously about a year after he left. Never did work out what triggered it.

I recognise so very many of the things you describe. How relieving it is not to be working everything around him.
How you and the kids just slot in together like a well oiled machine.
You are doing amazingly and don't let anyone say otherwise. It does get easier, It really does.

I spent 6 years on my own with the kids afterwards, best thing I ever did for me and for them.
9f course everyone is different and that may not be your path, but it sounds like you have this, so good on you.
Al the best.