The he "never has treated me as a slave" will never sound natural to me, it always feels like a lazy excuse just to try to justify the slave trope fetish, because if he is "good" then that makes it ok, isn't it?, let's just pretend that he didn't acquire her like an item in the first chapter and right away slept with her, surely is because she really loved him even tho she didn't know anything about him... If you are going to have a slave trope in your harem manga don't try to justify it, it will make you look dumber, we all know why it's there.