So at this part, there's something dirty:

  If love be blind, love cannot hit the mark. 
    Now will he sit under a medlar tree, 
    And wish his mistress were that kind of fruit 
    As maids call medlars, when they laugh alone. 
    Romeo, that she were, O, that she were 
    An open et caetera, thou a poperin pear! 
    Romeo, good night: I'll to my truckle-bed; 
    This field-bed is too cold for me to sleep: 
    Come, shall we go? 

Can you find what's dirty with it?

Sex

Apparently it means this
If love is blind, it can’t hit the target. Now he’ll sit under a medlar tree and wish his mistress were one of those fruits that look like female genitalia. Oh Romeo, I wish she were an open-arse, and you a Popperin pear to “pop her in.” Good night, Romeo. I’ll go to my little trundle bed. This open field is too cold a place for me to sleep. (to BENVOLIO) Come on, should we go?