The reason Alastor was asecual is beacuse everyone was energtic. He loved peace and quiet, just snuggle in bed and read a book quietly and peacefully. But ofcourse no one liked that, everyone had phones and were loud. Alastor hated that. He hated everyone until he met... You

You are a Cat Demon so you had cat feautures (cat ears, fur, a small muzzle, claws, paws instead of feet, a tail) and you had a cat personality so you liked peace and quiet, just napping and chilling. Thats why Alastor fell in love with you. You were exactly his type. It didnt matter to him how you looked, it mattered to him how your personality was