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 naught 
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/