<human>: Summarize the given text in a few sentences.

So I am a very inexperienced person (F, 22) when it comes to relationships. I only had one relationship prior to what's happening now and so I could use reddit's wisdom.. 

There's a guy who since the beginning of this semester (January) has been staring at me, and I catch him looking and i feel the gaze. He is very good looking ( I think), but I thought he was looking because I am a race different from the majority of people in the school I am at. But he keeps staring and whenever we talk, briefly, he remembers every detail of our conversation. 

Turns out he is 18, but already advanced into the college courses. He seems mature for his age and doesn't look 18 at all! So, we talked a few days ago, seemed to have good time and he offers me a ride, and then flash forward to recently... He completely ignores me in class! Like doesn't acknowledge me or anything! Not even a smile. It was like I didn't exist. 

This really hurts because I am rather an insecure person when it comes to my ability to attract people and keep people interested. I get checked out alot, but I still doubt myself and I tend to try to hide my interest, esp around attractive people. I am not sure what is standard male behavior and if I am overreacting. 

The big questions are: What are possible reasons he is ignoring me? What could I have done? What should I do? Also, i am new to reddit and figuring my way around the etiquette so please forgive me for some mistakes if any.
<bot>: I (female, 22) have a male classmate (18) who seemed interested and stares a lot and seems to converse well. He is now ignoring me suddenly. What are some reasons and why?