I struggled to 'reframe' and understand my (ex) marriage. I had a very happy marriage to start with (and for many years) but he changed and became abusive. The 2nd stage of the marriage crept up on me so that I didn't recognise it as abusive until I'd left.
Then it seemed a tragedy and I wondered how long I'd been in such a sham and travesty of a relationship. It really hurt and made me question everything. I felt stupid, grief stricken, regretful at the wasted years and lacking in confidence in a future.
Eventually I realised that my marriage had been happy, had been good. I have 3 lovely DC and some good memories. Its ok to miss that marriage. It is a bit like a bereavement and loss. You can mourn what you did have. It doesn't mean it was bad. It changed, which is the sad thing.
I think to begin with, its not really possible to view the past in this way because it makes the loss even more painful. You switch between mourning and hoping to go back to what you had and then in recognition that you cannot...you start to view it badly.
It will take time (sorry) but you will get to a happier place. I think you will fight your way through faster than many, because you don't shy away from difficult stuff. It is exactly that gutsy nature which is making you suffer in some ways but I think you will come through healthier (mentally) because you're confronting it rather than sticking your head in the sand.