ahhh... the insecurity of young love! I'd say it sounds like he's into you, and he gets quiet because he's afraid he'll say something to embarass you in front of others, or say somethign to give his true feelings away before he can bring himself to tell you about those feelings himself.

How about renting one of those movies where the couple are best friends forever and suddenly realize they are in love? You can watch it together and see if he reacts!