I need an explanation for the 'Forbidden Mourning' poem. it's a great piece of work.?

Question

In simple English, can anyone explain the lines of this poem?
Our two souls therefore, which are one,
Though I must go, endure not yet
A breach, but an expansion,
Like gold to aery thinness beat.

If they be two, they are two so 25
As stiff twin compasses are two ;
Thy soul, the fix'd foot, makes no show
To move, but doth, if th' other do.

And though it in the centre sit,
Yet, when the other far doth roam, 30
It leans, and hearkens after it,
And grows erect, as that comes home.

Such wilt thou be to me, who must,
Like th' other foot, obliquely run ;
Thy firmness makes my circle just, 35
And makes me end where I begun..

Answer 1

http://www.sparknotes.com/poetry/donne/

Answer 2

John Donne is a tough study because we cannot readily put his words into a context we understand for today.

This may help:
http://www.bookrags.com/studyguide-valediction/sum.html