People whose partner watched hentai, how did it affect you? I want mine to understand.

Hi everyone. I don't know if this is a typical post for this subreddit, but I'd really appreciate some outside perspectives because my boyfriend and I have reached a complete standstill in this discussion.
A while ago, my boyfriend admitted that he had watched porn a few times during our relationship. During that conversation, he eventually agreed that watching porn featuring real people crosses the line into cheating because you're directing your sexual attention and energy toward someone outside the relationship.
Now we've started discussing hentai and other forms of animated pornography, and that's where we completely disagree.
His argument is that hentai isn't cheating because the characters aren't real. According to him, they're "just pixels," and because they aren't real people with thoughts or feelings, fantasizing about them or masturbating to them isn't the same as watching porn with real actors.
My perspective is completely different.
To me, monogamy isn't only about physical exclusivity. It's also emotional, mental, and sexual. When you're in a committed monogamous relationship, I believe your sexual desire, fantasies, and sexual energy should be directed toward your partner rather than someone or something else.
For me, it doesn't matter whether the object of attraction is a real person, a fictional character, an anime character, or an explicit drawing. What matters is that my partner is choosing to become sexually aroused by something that isn't me.
Our discussion eventually turned into a debate about what actually makes something "cheating."
His argument was that if the other party isn't capable of feeling anything toward you because they aren't real, then it can't be cheating.
My response was that this misses the point entirely. I don't think cheating is defined by whether the other person can reciprocate feelings. I think it's defined by the actions and intentions of the person who made the commitment.
To me, the important question isn't whether the hentai character can feel anything. It's whether my partner is directing his sexual thoughts, fantasies, and arousal outside of our relationship. That's what feels like a violation of monogamy to me.
I'd really appreciate hearing from people who have experienced something similar.
If your partner regularly watched hentai or other animated pornography, how did it make you feel? Did it affect your confidence, your trust, or your relationship? Did you personally consider it different from regular porn, or did it feel the same?
I'd also appreciate hearing your thoughts on the discussion itself. Do you think the fact that a character is fictional changes whether it's a form of infidelity, or do you think the focus should be on the committed partner's choices and where they're directing their sexual attention?
I'm genuinely looking for respectful opinions from both sides because I'd like to understand how other people see this.