beta
The Duke fell in love with an idealized version of Alicia and doesn't actually know anything about her.
Chase met Alicia and naturally grew to be her friend and confidante as he fell in love.
If you planned for one person to be the ML, but the other ends up having better chemistry with your FL you might want to just go with the flow, rather than rigidly cling to the story you initially thought up.
Its like the author had 3 isekai concepts in their head and they just smooshed them all into one, rather than writing them all individually.