I built my house beside the wood
So I could hear you singing
And it was sweet and it was good
And love was all beginning
Fare thee well, my nightingale
'Twas long ago I found you
Now all your songs of beauty fail
The forest closes 'round you
Since Cohen called himself a “broken-down nightingale” ( Source ), he could refer to himself and the end of his singing career.
Nightingale