so the hero isn’t evil, but cursed by the same demon she and MC (the sage) defeated, MC poses such a threat with his ability to learn magic that the curse/demon is trying (by use of the hero) to force him to regress or at the very least stunt his insane growth. That’s why the hero started to change, it wasn’t jealousy, she wasn’t like that in childhood, but a curse/demon trying to sabotage the MC, and effectively ruining any chance of a healthy relationship between the two. Unique take on the “kicked out of the hero’s party” trope and i’m interested to see more.
Tsuihou no Kenja, Sekai wo Shiru ~Osanajimi Yuusha no Atsuryoku kara Nigete Jiyuu ni Natta Ore~