After the girl confessed to the boy, why didn't the boy reply to her message?

I am a boy. In my opinion, he has two possibilities. One is that he doesn't like you and intends to break up with you. The other is that he used to get along with you like friends, but now he feels a little embarrassed to give it back to you. He doesn't know how to get along with you. It depends on what kind of person he is at ordinary times.