How can I stop my brain from going spaz over a guy at school?

I really like a guy at school, and I know the attraction is mutual. We're definitely in different places as far as interest, though, and I am trying to figure out a way to stay friends, and keep the door open on a future relationship, without either coming on too strong, or making a series of dramatic gestures along the lines of "I'm better off without you anyways" (which is pretty much just a tacit admission, for me, that I've spent way too much time thinking about him, and not enough time actually talking with him.) Since I've read far too many relationship books, I now have a tendency to waiver between obsessed schoolgirl and frigid ice queen when a guy doesn't show a uniform level of intense interest at every moment we're within 20 feet of each other. They really should have rehab for that sort of thing, but barring that, I'd like to just come off as a fairly sane person, and be cool when we're hanging out, without coming off as expecting too much because we talked for five minutes. I'm remarkably chill and non-dramatic about it until I actually get around him, at which point some insidious organ in my brain starts playing a medley of sweeping orchestral interludes from every romantic comedy I've ever hated. I'm not sure what I need for these types of situations (breathing techniques, a mantra, Valium...?) but if anyone has any ideas from previous experience, I'd appreciate any advice.