Sonnet from the Portuguese--- Love ?

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 ... for a trick of
thought; That falls in well with mine,
And certs 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, since one might well
forget to weep who bore thy comfort long,
and lose thy love thereby.
But love me for love's sake, that evermore
thou may'st love on through love's eternity.