This is not a passage that pines for what is not.  It is stating how things are -- pain and joy are indivisible -- and thoughtfully resigning to this as better than being without pain, and so without joy.

How do you read it?

CR Mittal wrote:
[log in to unmask]" type="cite">
looking before and after and pining for what is not
Yet if we could scorn
        Hate and pride and fear,
      If we were things born
        Not to shed a tear
I know not how thy joy we ever should come near.
        -- P.B. Shelley, "To a Skylark"