Also, Hitogami told Rudeus he'd regret leaving.
Last week I thought that was Paul dying and seeing Zenith as she is.
What if something also happened at home while he was gone, something only Rudeus could have prevented? Hope Sylphiette isn't the victim.

Regarding polygamy, I think I remember Sylphiette telling Rudeus she did not mind him having several wives.
But maybe once she's confronted to that reality, she will change her mind.