If I look at other women, all it does is make me question more why I should give up (Rosalind). No woman can compare to her. The remainder of the speech beginning on line 237 (which is this one), compares her to that are passing fair, and Romeo comes to the conclusion that Benvolio has nothing to teach him.
In short, looking at others will only make him compare and pine even more deeply for the fair Rosalind.
So that line in modern English would read
All comparison does is make me appreciate her beauty that much more.
