I’m so sorry you’re going through this, 53 years of marriage is a lifetime and it’s bound to take you a long time to adjust.
Try to take things in small manageable chunks.
Just focus on the next small step so one phone call, email, one appointment, one task for each divorce stage & the house. Has the GP suggested anything to manage the depression? Have you had any counselling? What about a support group?
You need to detach from thinking about him. My ex moved on with another woman who I think ( but still don’t know) overlapped with me. It was laughable taking photos of themselves blown up into a large canvas and framed pictures all over the house. However quite soon problems set in and then the photos and that relationship disappeared. But you are free of someone who was violent. Have you done all the things that symbolise moving on, changing bedroom furniture around, changing type of bed linen, booking a holiday, even getting a pet you’ve always wanted?
Also have you read Belle Burden’s book “Strangers a memoir of a marriage”? I recommend it. The book (and an essay she wrote for The New York Times) explains the sudden end of her twenty-year marriage following her husband’s affair and sudden decision to leave. One of the many useful things was a metaphor that her therapist stepmother used .. basically it involved imagining her and her husband on a stage and moving the spotlight away from him to her..The more you focus on his apparent happiness now or even his past violence, the more you are controlled by it. It may look as though he’s happy and carefree now but he won’t be. You may feel flat because when you’ve been in a difficult marriage, there’s also complex biology about your body sort of getting used to the highs and lows of cortisol or Adrenalin or whatever it is.
You have been through a lot, and surviving to where you are already shows your strength.