the first half of the title. the second half of the title is about going to school and not raping heroines which is probably why they time skipped the weight loss arc so we can get to the main setting. I'm sure there will be some explanations of the otome game plot that will show fat Karl again
They could have at least made him look big but mobile in a month to reflect transition. People still would have probably said he was heavy and could have pushed more diet ideas between the arc.
I can see he was just giving you a playful hard time on choice-of-word, since as it's used, fiancé is the masculine use, while fiancée is the feminine one. Any issues you want to bring up, bring it up with the French.