Who is Shakespeare referring to when he says "his" in the line "within his bending sickle's compass come" in Sonnet 116?

The answer to this question comes just a line before, when
we are told who "his" refers to. Often a lot of the meaning of lines can be understood
if you take them in context and read immediately before and after to make sure you
understand what is being referred to. Have a look at these
lines:

Love's
not Time's fool, though rosy lips and cheeks

Within his
bending sickle's compass
come.

In these lines
therefore, the speaker of this sonnet alludes to the medieval image of time as the grim
reaper, who cuts off life with the sweep of a sickle. Notice the point that the speaker
is making - although youth is clearly under the power of Time as we all age, yet Love is
not "Time's fool," meaning Love does not alter or change as we grow old. This of course
ties in to the overall theme of this sonnet, which is the permanence of
love.