You're right. I read the whole novel and I know Ian's motivations and past but I still can't forgive him completely for what he does to Michele, a completely innocent person, that despite everything is ready to love and cherish him fully. He should kill anyone that hurt him directly but it gets to me that he chose to mentally torture and take advantage of the only person who was in the womb/barely even alive when the worst was happening to him.
As someone who absolutely loves Ian's character, I actually agree with you. His past doesn't justify how he treats Michele. Michele is innocent and has been nothing but sincere…he doesn't deserve any of it regardless of what Ian has endured. I also understand your frustration with comments that seem to minimize Michele's suffering. I just think there's an important distinction between understanding his actions and justifying them. For me, learning about Ian's past was never about excusing his cruelty but understanding the deeply wounded, distrustful, and contradictory person he's become.
And while revenge may have been his initial motivation, his relationship with Michele becomes far more complicated than simply punishing an innocent Anatold for his family's wrongdoing. Michele challenges so much of what Ian believes about people, affection, and even himself, that it leaves Ian struggling with feelings he neither understands nor knows how to accept. I appreciate the character’s complexity without condoning his actions.

I see a lot of comments pointed out that Duke Shelleg is being a jerk (finally). And they have been replied to, saying that it's because he had a traumatic childhood. Well if these people did not know about it before, I'm glad you shared the information you had. It helps get more context of the story. But half of these replies lowkey seem like they wanna justify him so much. As much as my heart hurts for all that he went through, it will never change the fact that he's being a dihh. "oh it's not that bad comparably", "oh he's just human" I KNOW KATIE. I know well enough where he's coming from, but what is wrong is wrong. Boy could have killed his perpetrator and tortured him for all I care, but I'll forever hate him a little for putting another innocent person through all this. The context, the reason, the relations, the emotions- none of them will change that. Imagine your father did do something horrible (for which he should be punished), but the victim targets you or your other loved ones instead although your father himself was also a jerk to you. That's still fucking unfair despite how much you understand the aggrieved party