Edna St. Vincent Millay 

Oh, think not I am faithful to a vow !
Faithless am I save to love's self alone.
Were you not lovely I would leave you now:
After the feet of beauty fly my own.
Were you not still my hunger's rarest food,
And water ever to my wildest thirst,
I would desert you – think not but I would ! –
And seek another as I sought you first.
But you are mobile as the veering air,
And all your charms more changeful than the tide,
Wherefore to be inconstant is no care:
I have but to continue at your side.
So wanton, light and false, my love, are you,
I am most faithless when I most am true.