Answer:
There are a few metaphors in this passage and they are about various things. Each of the quatrains have something particular about them. 1 - his age is a time of year ; 2 his age is like late twilight, and in the 3rd - he compares himself to the glowing remnants of a fire...
He is advancing in age. In winter the man feels old age like cold in his bones. Then the age is compared to twilight - going slowly
He is explaining that death can be a slow process, but you must understand that you will die some day.
Step-by-step explanation:
he must perceive these things and his love must be strengthened by the knowledge that he will soon be parted from the other person - like a fire that is extinguished slowly. dies out. death.