She allowed polygamy, she knew what she was getting into.
People don't necessarily make sound situations when they're in love, and it's questionable to say she knew what she was getting into. Imaging something and thinking you can understand it isn't the same as actually experiencing it.
I'm scared to know but at the same time my morbid curiosity is getting the better of me.
The voice_actor_connection tag gave me a hunch, but it took looking at the source to figure out the precise details: so apparently the JP VAs for Subaru and Rudeus announced their marriage a bit before this was posted - turns out Rudeus is voiced by a woman, which I hadn't realized. Anyway, it isn't anything problematic, just some memeing on the situation via some of their most popular roles.