Bid adieu, my sad heart, bid adieu to thy peace!
Thy pleasure is past, and thy sorrows increase;
See the shadows of evening how far they extend,
And a long night is coming, that never may end;
For the sun is now set that enlivened the scene,
And an age must be past ere it rises again.

Already deprived of its splendour and heat,
I feel thee more slowly, more heavily beat;
Perhaps overstrained with the quick pulse of pleasure,
Thou art glad of this respite to beat at thy leisure;
But the sigh of distress shall now weary thee more
Than the flutter and tumult of passion before.

The heart of a lover is never at rest,
With joy overwhelmed, or with sorrow oppressed:
When Delia is near, all is ecstasy then,
And I even forget I must lose her again:
When absent, as wretched as happy before,
Despairing I cry, I shall see her no more!

William Cowper

http://www.poemhunter.com/poem/on-delia-bid-adieu-my-sad-heart/