Being your slave what should I do but tend, 
Upon the hours, and times of your desire? 
I have no precious time at all to spend; 
Nor services to do till you require.  
Nor dare I chide the world-without-end hour, 
Whilst I (my sovereign) watch the clock for you, 
Nor think the bitterness of absence sour, 
When you have bid your servant once adieu. 
Nor dare I question with my jealous thought, 
Where you may be, or your affairs suppose, 
But like a sad slave stay and think of nought 
Save where you are, how happy you make those. 
So true a fool is love, that in your will, 
(Though you do any thing) he thinks no ill.
William Shakespeare
http://www.poemhunter.com/poem/sonnet-57-being-your-slave-what-should-i-do-but-tend/