Cornwall didn't set up the Elvish slave thing. That would have been the "Crusaders" who found this new continent, who purged and enslaved the Elvish population.I somewhat trust him. If I remember correctly he is the one who set up the whole elfish slave thing. So unless the MC threatens what he built, he is relatively safe. Next point is that Cornwall has seen how the MC treats his slave(s) so the risk of him taking them away is minimal at the moment.
I just don‘t like him thinking about giving love to all those sweet elven girls out there. That‘s my job. I mean... the MC‘s job.
Regarding Elven politics, the player knows that everything for Elves changed roughly 20 years ago, Autumn's father was the reason behind that, and Cornwall has the ability to take away anyone's slave.