because as the asshole ML said in the newest chapter, chapter 10, not only will he have a child with MC but he will also use MC as a way to release his pheromones and keep them at a stable level, and that can only be done by having sex, also MC will have absolutely no power in making decisions like using IVF, so they will be having sex
As far as I remember - that was NOT part of the contract. MC is not contractually obligated to aid scumbag ML with his shitty pheromones .
I feel like MC / could/ make the argument and fight against having physical sex , but they're not headstrong enough of character &stubborn to do so, too paranoid of the truth of his daughter being found out & worried about immediate situation instead of thinking ahead & planning
But whatever
Drama, smut, tension
I don't have high expectations for this story anymore

Does IVF not exist here?? Why do they have to fuck?
Just collect sperm from scumbag donor