Analysis of The Computation

For the first twenty years since yesterday
                  I scarce believed thou couldst be gone away;
            For forty more I fed on favors past,
               And forty on hopes that thou wouldst they might last.
                    Tears drowned one hundred, and sighs blew out two,
               A thousand, I did neither think nor do,
               Or not divide, all being one thought of you,
               Or in a thousand more forgot that too.
          Yet call not this long life, but think that I
               Am, by being dead, immortal. Can ghosts die?