I'm an idiot
I just watched this film for the 2nd or 3rd time having a passing familiarity with the play and i just noticed that Romeo was pining for another woman at the beginning. I always thought that he had already seen Juliet and that's who he was referring to when he said he was in love.
To be honest, that kind of lowers my opinion of Romeo a bit. How do we know that what he felt with Juliet was true love? If he could have such strong affections for Rosaline the way he was waxing poetic at the beginning and then immediately abandon them when he sees Juliet, how do we know that, if they had lived, he wouldn't have fallen in love with some other girl 6 months later?