<?php
$previous_post=null;
if ( have_posts() ) {
while ( have_posts() ) {
the_post();
global $post;
if($previous_post!=null)
{
/// Do what ever you want to do with previous post $previous_post.
}
$description = get_post_meta( get_the_ID( ), 'metabox_description', true );
echo $description;
// Add: echo $description_from_post_before;
$previous_post = $post;
} // end while
} // end if
?>