I suppose Hitogami's advice was to ensure that he wouldn't miss out on a potential reunion with his childhood love (also the implication of how he will get over his ED). Even with divine advice against doing the "right" thing to reunite the family, it's feels like hamfisted writing and not what the character would actually do. Rudeus barley trusts Hitogami as it stands.
I feel that he trusts him enough to follow his advice though.

As for his magic, he probably hasn't studied it much since then. He can cast spells quickly, without enchantment and he doesn't seem to be bothered by mana limits during routine use - but I can believe that he hasn't learned anything more groundbreaking since then. His application in battle is still top notch.

I share the kicker about Zenith though. At the end of last season, it seemed like she was trapped underwater in the Labyrinth country.

I'm glad we're finally at the academy. I'm hungry for more info on the world/plot.