The three places you mention are each significant to the conflict of the play. In the public streets, Romeo and Juliet are apart. I don't believe they are ever seen together, which is part of the point of forbidden love. They are seen together at the dance where they meet, but they are masked and therefore, no one knows who they are. However, the balcony and tomb are where they get together in secret. Perhaps if you look at the balcony as "high" up, you could equate or at least compare that to heaven, or heavenly. Then they end up in the tomb together which is a "low" place. They commit suicide, which would likely be looked up on as sending them both "below." I don't think there is a Heaven/Hell reference in there, but certainly the extremes are significant. Their deaths bring the two families together in the tomb, where they haven't been seen anywhere but the public streets for a long time.