This is one of my all time favourite poems. I love the last two lines, they stick in my head.

The want of you is like no other thing;
It smites my soul with sudden sickening;
It binds my being with a wreath of rue –
This want of you.

It flashes on me with the waking sun;
It creeps upon me when the day is done;
It hammers at my heart the long night through –
This want of you.

It sighs within me with the misting skies;
Oh, all the day within my heart it cries,
Old as your absence, yet each moment new –
This want of you.

Mad with demand and aching with despair,
It leaps within my heart and you are – where?
God has forgotten, or he never knew –
This want of you.

~Ivan Leonard Wright~