I can empathize with what he endured as a child, the abuse from his parents and the tortur...

I can empathize with what he endured as a child, the abuse from his parents and the torture he later suffered under the emperors orders. His life was marked by pain and betrayal (clearly there was a conspiracy against his house). But his past doesn't erase his crimes. It can't justify the way he treats a woman who is faultless in his suffering, a woman who genuinely loved him and even helped him.
His behavior is not born of love but of selfishness and obsession. He channels his hatred of the emperor and her family into her, weaponizing her loyalty. He manipulates her guilt, sexually abuses her, and deliberately breaks her until she becmes a fragile, compliant shell of her former self, a fucking doll he can always access and control.


Major spoiler ahead:

In the manhwa this abuse is depicted, but in the novel it's even more explicit.
Her first experience with him is a brutal rape. He
"rescues" her from a forced marriage to a fifty yearold man, something arranged by her own brothers (that want the throne), but his salvation is nothing but a creepy ass opportunity for him, he literally tells her "Either live sucking my dick or kill yourself. Those are your only options". She of course chooses rape because it's the only way to survive.
At one point he even says, while raping her, "Maybe it shouldn't just be me enjoying this hole. Such a waste, maybe your subordinates should have a taste too", degrading her.
All of this cruelty stems from a misunderstanding because he believes she agreed to send him to the border, even though it was solely her brother's order. He forgets everything she has done for him, everything she sacrificed, and takes her loyalty for granted. The suffering she endures is the direct result of his filthy mistrust. Eventually she reaches a breaking point. She wants to die, to leave her place as empress. Only when he loses her does he realize too late that he truly loves her. Regretful he begs her to punish him, and she does until he is groveling on the floor, asking for forgiveness.

I won't spoil any further details. But the story is a devastating portrait of how trauma can twist someone into a monster and how, in the end, remorse is often not enough to undo what's been done.