I know it's a bit crazy, but it's not impossible... Who hasn't fallen in love with their female professor?
- He could have seen her trying to sabotage and harm him as a direct challenge, something very few people probably dared to do.
-He liked it very much. It's not every day that a woman faces the demon lord.
-Emilia is very beautiful before and after becoming mixed-blood, and Anos enjoyed her classes.
-He fought with her brother, something very unusual for a low-ranking student, perhaps to get her attention.
-He forgave her for attacking his mother and her fan club (but he gave her a fair shake).
-He made her mixed-blood even though he knew everything that would happen, he probably wanted to save her.
-It's no coincidence that if her mother rescued her, she ended up in his house.
-Anos forgave her and even offered her a position at court.
-Emilia redeemed herself and was supported by Anos disguised as a boy, something he perfectly didn't need to do and could have simply ignored her, but he wanted to save her.
-Why? Who knows.