How is Romeo and Juliet's love presented in Act 2, Scene 2, line 33?

That's a tough question, because line 33 is part of a sentence that extends from earlier lines and into later lines.  Using only line 33 is hard because it is being taken out of the overall context.  Line 33 is the following:

Of mortals that fall back to gaze on him

Too many questions surround that line.  Why are mortals falling?  Who is the "him" in the line?  
 
Let's look at the entire sentence instead.  


O, speak again, bright angel! For thou art
As glorious to this night, being o'er my head,
As is a wingèd messenger of heaven
Unto the white, upturnèd, wondering eyes
Of mortals that fall back to gaze on him
When he bestrides the lazy-puffing clouds
And sails upon the bosom of the air.



Act 2, Scene 2 is the famous balcony scene, and the above lines take place before Romeo and Juliet start talking to each other.  Romeo is looking up at Juliet, and she doesn't know he is there.  You can decide if that is creepy or not.  
 
Line 33, and its surrounding sentence, is being spoken by Romeo about Juliet.  He is comparing her and her beauty to an angel of heaven.  He looks upon her with amazement and wonder, which is how he imagines that he would be looking at an actual angel of God sailing through the sky. 
 
Understanding the line in that context causes me to see their love for each other presented in a specific way.  Their love is being presented as cosmic, godly, angelic, glorious, and/or heavenly.  Line 33 shows that Romeo isn't quite certain that mere mortals are supposed to have these kinds of feelings, yet he is witnessing something (Juliet) that appears to be straight from heaven.