Cassy, I don't remember ever reading this, but it doesn't mean JJ didn't say it. Do you have a link?
The way the actors played it, it seemed to me that they were already lovers...or certainly IN love with each other, requited or otherwise. The scene in the shuttle hanger certainly implies a sexual relationship. Also, their interactions and body language in most scenes seems to support a serious relationship(e.g. as Spock hurries from the bridge to beam down to Vulcan).
When I first saw the movie my first impression also was that they were in a serious relationship before getting on the enterprise. Perhaps, though, they were in love and just hadn't become romantically involved yet? I'll try to find the interview and post a link for you.