He didnt want kids, she wanted kids. Due to regency societal expectations she didnt completely understand the pull out method and just thought he was infertile. She feels decieved.... So one night he gets drunks and she gets on top and doesnt allow him to pull out. 

Its messy. It kinda sexual assault. I am unsure how this series got as big as it did and a Netflix deal if this is the starting point.