If thou must love me, let it be for nought
Except for love's sake only. Do not say
'I love her for her smile--her look--her way
Of speaking gently,--for a trick of thought
That falls in well with mine, and certes brought
A sense of pleasant ease on such a day'--
For these things in themselves, Beloved, may
Be changed, or change for thee,--and love, so wrought,
May be unwrought so. Neither love me for
Thine own dear pity's wiping my cheeks dry,--
A creature might forget to weep, who bore
Thy comfort long, and lose thy love thereby !
But love me for love's sake, that evermore
Thou mayst love on, through love's eternity.

Elizabeth Barrett Browning

http://www.poemhunter.com/poem/sonnet-xiv/