I need advice on a boy..?

Okay there's this boy and we see each other pretty much everyday, He's only a year older. We really talk a lot 2 times a week but we see each other 5 days a week. Today we were in a meeting, and He came up to me n said "Mmmm, Lookin great today." Then In the middle of the meeting I was sittin ontop of the desk and he walks over and puts his arm around me, n says "This is my girlfriend." and smiled at some of his friends. Okay, Now I'm the type that I dont wanna step forward and ask him out because I don't wanna get rejected but I really like him!!! What do I do?????