You can understand but still not justify him. His actions aren't justified in any way, his backstory doesn't really change what he did, it just gives us a glimpse over his circumstances, it gives as an explanation over his emptional state and his trauma. I've read the novel, it's good but it's realistic. It doesn't sugar coat that he has been a monster to her without ANY justification other than his incredibly flawed and destructive view. Even after they get back together, fl never completely heals. Being a victim doesn't give you a pass to abuse someone else. That's why i don't blame people hating him for what he did. He is a detestable character and plenty of detestable characters have also been victims themselves. He's just not a one dimensional villain, he's human and has gone through suffering. He has being a victim but he has also been the abuser, damaging another human being irreparably the same way he was damaged irreparably. Hating someone doesn't necessarily equal not understanding them.
Like I said I couldn't never understand why he acted like that even if he has trauma because I didn't experienced the same so I can't really say anything not knowing how myself I would reacted...I don't judge but I will just accepted that they are both victims. You know because we are human we cannot predict entirely how we will react in any case so I m gonna be neutral about this subject
Not understanding or understanding someone over what lead them to do a certain action, doesn't change the said action. Even if you acted the same in his shoes and could completely empathize with what lead him to this, it would still be by definition abuse towards another human being. Trauma doesn't excuse abuse. I'm not saying that i myself would 100% be a better person, because like you said, you can't know. But i would still be considered abusive to another if i behaved as he did. Being a victim doesn't excuse abuse towards another. No one denied that he's
a victim. What people are saying is that he's also clearly an abuser and that's in front of your eyes to observe. Trauma doesn't shield you from consequences nor does it take away the pain you have caused to another. Did you know that the biggest percentage of child predators have been sexually abused in their childhood? Do you think their trauma makes them will shield them from the consequences of their actions, one of them being judgment over their abuse towards children? What I'm trying to say is that, whether you understand someone's reasons or not, you can define what is a horrible action or not.
Like I said before,I wont judged any characters before the end because everyone has his own circumstances...and after I learn about the novel I can say the husband and his wife are both victims... it's really a sad story , you need to understand psychology how trauma can lead any person to this kind of situation...