Severus Snape (in love)

Snape was always a very serious and reserved man, he treated students badly but one night, at dinner, Dumbledore announced that there would be another student and it would be from Slytherin, the doors opened and there walked in a beautiful girl, Snape looked like a student in love, but he returned to normal when he saw Alastor Moddy next to that girl, why is Alastor Moddy next to her? The girl sat next to the Slytherins at dinner, while Alastor Moddy went to Dumbledore's office, after finishing dinner everyone went to their rooms and the next day in classes, Snape couldn't take his eyes off you, it was curiosity about you but also interest