I'd hazard a guess they are both lying to some sort of degree, and both being honest to a certain degree.
Because as the old saying goes
There's hers, his and the truth...
My personal opinion is they both abused eachother to varying degrees. I cant tell you which one was worse because I'm not fully briefed with the evidence. I'd guess there wasn't a typical one was always the aggressor and one was the victim constant. I think it was a circle of toxic behaviour.
One did something that upset the other intentionally by DA or unintentionally or due to substance misuse or due to poor mental health or all of the above, the other retaliated (in some form, physical, emotional, psychological abuse, causing fear) and then they both went at it hammer and tong till it burnt out and settled down, and round and round they went.
It was horrific for all I'd imagine. And regardless of who hit who first, or how many times one hit the other under any circumstance it was still wrong.
I am inclined to believe that JD experienced his fair share of psychological and physical abuse by AH. I fully accept that, but I also accept that during these "disturbances" that AH may also have experienced physical and psychological abuse.
Till eventually, and credit here to JD, I think he was the one who said "enough is enough" this is wrong, this can't go on, and ended it.