Been in a similar place. My ex spent the last two years of our relationship, being quiet seriously abusive. Mostly physically and mentally but there were a couple of sexual assaults.
Yet the night he left I fell to the floor and literally begged him to stay.
Feeling lost and empty is normal. The end of a relationship is ALOT like grieving, only problem is the other person isn't dead. And there is always the 'what if' hanging over your head.

Are you two officially over, or do you want him back, does he want to come back?

It may not feel like it right now, but with a little support you will wake up one day and realise he isn't what you want.
Please access any support services for battered spouses. And any Mental health resources that are available.

For a long time I kept talking to my ex, kept trying to make him understand, how badly he had hurt me. And our kids. How it had been unnecessary. That he could have just talked to me.
I wanted to see some remorse, to hear an apology, that maybe he was ashamed.

Problem was, he wasn't and didn't, because in his head it was my fault, and NOTHING was going to change that.

It was when I finally clicked, that he absolutely believed that he wasn't at fault that I was able to start moving on.
I realised whatever we had was broken beyond repair and actually, I didn't want it back.

It can take time, and like you I had severe panics and flashbacks.
I wasn't so much taking it a day at a time as, 15 mins at a time.
If I tried to plan further ahead than that I had a full blown panic attack.
Baby steps, one at a time. If yo successful, congratulate yourself, if you can't do it this time, it's ok. Just move on to the next mini task.

I wish you all the best. Take care.