a true sentence

A true sentence 

As Hemingway said, start with a true sentence
the roof of the school building, I can see from 
where I sit on a cloudy day is grey as lead
when lit up by sunlight that has broken through 
the clouds, it turns silvery and pleasant to see
That is, a true sentence about what I see, but it
is not what I'm thinking is a love story that
began a summer's day, lasted with its drama
when days got shorter and the wind bitter
leaves shrunk and fell on a rainy street
The true sentence is the gripping sadness
the knowledge that the best of my time has gone