Nah this is actually so fun; I love it when an isekai protagonist can be honest about their situation from the get-go. Also him accidentally romancing the cut-content dark route is such a good twist
The whole line about "[...] in reality, I'm actually not his servant..." as a cliffhanger is a bit odd to me, because, if anything, losing the servant-master dynamic would be a boon for them relationship-wise. But I wonder if its more about why he's posing as Arthur's servant specifically?
He's mentioned a few times that Arthur's mind is fairly weak; i wonder if he maybe used dark magic to make the original Arthur take him with him to school for some plot purpose to his cut route? I was wondering why he was even his servant in the first place, since the original Arthur seems just like a weird guy to follow around