What does this verse from Romeo & Juliet mean?

[annaaa katherine?]

p.451 Juliet:
Give me some present counsel; or, behold,
'Twixt my extremes and me this bloody knife
Shall play the umpire, arbitrating that

line by line translation please would be extremely helpful

 

[Kitty Kat]

give me some advice or, watch,
between my extremes and I this bloody knife
shall play the umpire, judging that