what was it about annette that made sebastian fall in upendo with her? and why was katherine so threatened kwa it?

he fell in upendo with her because she proved she was zaidi than just a challenge, she taught him how to feel, how to smile, how to have joy and happiness in his life. and kathryn was jealous because now that sebastian had annette, she was truly alone. and this is just my view on the whole thing but, i think kathryn was in upendo with sebastian, thats why it hurt her so much to see his journal in the end, probably why she was using koki (to deal with actually feeling upendo for somebody), and why she was so upset to the point she was ready to ruin sebastian for falling in upendo with annette. it all makes sense if wewe just pay attention and read between the lines(:

kathryn was so jeaoluous because seabstian found his first true upendo and she don't was that girl.
She loved Sebastian but he cahnge her mind and then she didi't upendo her.
She loved annete not only phisycally like kathryn
he fell in upendo for the first time