Class and sit across from each other and they some times talks evn though they dated for 3 weeks?

There is no way anyone here can answer that with the lack of detail that you included.

Maybe he likes you. Maybe not. Should he still be in the same class if he doesn't like you? Of course. Should he talk to you? Why not?

See? We don't know him or you as we are not there. You will maybe just have to ask him. And really though... 3 weeks? Do you still care about this guy for just 3 weeks of dating?