How often is it normal to have a boner??!!

I come out to the living room(where my boyfriend is watching a movie) in a sexy school girl costume that barely fits, do some sexy poses, & bend over a bit. Hes smiling, and telling me he likes it, checking me out. Next I come out in a sexy nurse outfit, very short skirt, nurse hat & gloves, and pasties... do some more sexy poses & he chases me back to the room where i'm changing. Now I come out in an oversized button t-shirt & panties... I am all over him, shaking my buttoks, running my fingers through my hair & all. After all this he does not even have a hard on. I know that he definately liked it, but is he not very sexually attracted to me or something?? We're both young and sexy, so I am a little bit worried... and not to mention sad. Is it normal for him to not be excited??