Feferi wasn't a bad Moirail. She left Eridan because she was tired of him not listening to her. She tried to stop him from hating the land trolls and going forward with his genocidal tendencies and he never listened. That's why she left him. They were hatched for eachother yes but that just means they were born into their Moiralliegiance roles, Eridan being born to protect Feferi like a knight protecting the Princess, as opposed to developing real pale feelings.
yes, but it’s also a moirails job to soothe the other, to keep them pacified and non-violent. Considering Feferi had Eridan killing lusii for her, I’d say she didn’t do a very good job.
~Mod T